I try to avoid the rifle comparisons, as these PCC's aren't rifles (ignoring our legal definitions).  Again, they are a niche firearm much like the purpose of the M1 Carbine.  They are far easier to handle than a pistol (excluding CCW), more accurate and better range.  M1 Carbines did see front-line use, but their original purpose was aimed at support troops; a lightweight carbine that provided more firepower, range, and accuracy than a handgun.  I think that still applies in a variety of situations and it's a bonus that we have options.  If I'm outside tilling the garden, getting a load of firewood, checking trap lines, etc., I would much rather have the lighter PCC.  I still see it as a "handgun" and it would be used to fight back to my rifle, but PCCs are quite capable of decent accuracy and ballistics similar to your CCW/handgun at longer ranges.  Anybody using a PCC would hopefully understand the compromise and plan accordingly and I wouldn't expect them to fit all situations or be the perfect choice for every plan, but they can have a place for some people in some situations. I certainly wouldn't choose one if purposefully planning combat operations; however, I wouldn't feel under-gunned with one either...but tactics plays a bigger role than ballistics.  

I'm even more inclined with the "pistol" variants on the market and the inclusion of a an arm brace (ala SBR), as they still provide that stable platform for longer distances and accuracy along with an even more compact and lightweight package.  Not all SHTF planning involves combat operations.  It's far easier to walk away from an accident or breakdown with my Sub2000 folded into a laptop-sized bag than my FAL hidden in a golf bag.  You could argue for a rifle-caliber pistol (AR, AK, etc.), and I wouldn't disagree with you...they fill the same role with a substantial increase in ballistics despite the shorter barrels...again, options are always a good thing.  Run a course inside 100 meters with a pistol caliber, pseudo-SBR, and you'll find a pretty amazing tool that fits between CCW and rifle.

ROCK6

One of the things you see pretty often after disasters or in the filed is the use of dissuasive fire. This is interesting because it has little to no role in military or law enforcement duty, but its rather common for civilian SHTF.
Back home its practically every week that a few shots are fired (safely) in the general direction of trespassers in farms and fields.  The idea isnt to kill anyone, just use the internationally accepted code for "GTFO my property". In the cases I've seen it used (semi-auto 22) it was the best way of getting people, in many cases very young children, from stealing crops or firewood out of the property and avoiding the legal PITA of a dead body in your property.
I know the internet commandos would ambush them, shoot them dead and bury them where no one will find them. What they dont get is that you'll be killing and burying a lot of people, or more likely end up in jail, because there thousands where those same poor bastards came from. After the big earthquake in Chile, a man spent nearly two thousand 12 gauge shells in a similar manner during several days after it hit dealing with scavengers and looters. More recently after the Hurricane in Texas there was a similar scene of an off duty LEO keeping looters at bay in a strip mall with dissuasive fire from a shotgun.
Not saying by any means this is the end all use of firearms, or that its likely to be applicable to specific scenarios/locations,  but it is something that clearly does happen, does have a role, and in that case, light and cheap ammo is clearly best suited for it. If anyone trying to second guess or happens to be armed, returns fire, or is an actual real threat in other ways, a slight change of point of aim changes it from dissuasive to effective fire.
Just some more food for thought.
FerFAL

Troops are just that, troops.  They are generally not far from resupply ability.  So a dead shoulder weapon means they'll get another one quickly, or at least their ammo can be used by the rest of his group.

The only benefit I see is ammunition logistics.  

In terms of size and weight ... a Colt 6720 with Aimpoint Micro T1 is very slim, compact, handy and effective.  I'd take 30rds of 5.56x45mm over any handgun cartridge.

For a little more weight you can have 20rds of 7.62x51mm in a Scar-17S.

In the "dissuasive" fire situation you describe ... the individual(s) is/are sheltering in place for a limited amount of time (assuming the situation gets resolved).  Should the situation be protracted, desperate people might resort to desperate measures.

This is to say, a Ruger 10/22 or Marlin 60 would be practical to "dissuade" undetermined looters.  Should the situation become more desperate / grave - having the ballistic capability to attend to marauders at greater distances requires rifles chambered in longer-legged cartridges.  The greater the capacity and speed of reload the better.  This is a situation where a handgun cartridge lever action or 9/40/45 semi auto would be far less than ideal.

Again, your stated situation had a lot of criterion.  E.g. an apartment dweller in Atlanta has a different set of requirements.

I think the point some are missing is that the purpose of the PCC/pistol combo is for purposes when you are away from resupply.

If a person is around the homestead and resupply and spare parts are readily available, then you obviously use the best weapon for the purpose.

When you are caught out and just trying to get home, you have no idea where your next resupply is going to come from, and E&E is the name of the game, not gun fighting, then I think commonality of ammunition and parts is of the utmost importance.

Most people carry a few hundred rounds of rifle ammo and maybe 50 for a pistol.  It would suck to have your rifle go down and be left with just a few pistol rounds to get home on.

I'm not picking on you, but I want to point out a few illogical issues here:

"E&E is name of game, not gun fighting ... commonality of ammo and parts is utmost importance".... if you're not using your gun except in dire self-defense ... now many rounds do you need (you said this isn't about gun fighting)?  Common parts?  For what?  If your gun can't make it through a mag or two without needing a repair ... you chose poorly.  

"It would suck to have your rifle go down and be left with a handgun" ... uhm, this discussion is about handgun cartridge weapons (and you're advocating them).  Why not ditch the handgun + handgun ammo and just carry more full power rifle ammo and a quality rifle?

Outside of the need to conceal a weapon (which would negate this entire thread ... PCC are generally no more or less concealable than an AR, AK, etc) I'll take a proven BCM or Colt AR-15 + 300rds of ammo over any PCC / Handgun + 300rds of ammo.  Add a Ruger LCP + 1 reload to my AR-15 and I still win.

When these conversations come up I always end up asking this ...

If you could arm your adversary ... which would option would you give him?  You want to arm yourself with the OPPOSITE gun (the one you wouldn't want your adversary to have).  Germane to PCC: would you rather face an adversary with a PCC or an AK-47?  I'd take the PCC adversary every time.

(side note: the same argument applies to 9mm vs 45mm, AK vs AR, 5.56 x 7.62).


ETA: The only handgun / rifle caliber combo that makes since is a 22LR carbine + handgun.  This particular combo is only sensible within the very narrow confines of an extremely protracted / isolated survival situation where you're not worried about defending yourself as much as feeding yourself.  I can easily carry 1,100rds of 22LR in a back pack (about 8# 3 Ozs IIRC).   Herein, the only advantage is the small / lightweight ammo.  PCC handgun ammo (9mm, 45Acp, 357, 44 Mag) isn't small or particularly lightweight and is weak compared to rifle ammo.  It isn't particularly well suited for hunting (ever shot a squirrel with a 9mm?) and therefore is basically defensive only.  Yes, you can argue a 357 or 44 PCC can be used for hunting larger game, but now you've sacrificed self defense performance (6 or 7 round lever action 44 against an adversary armed with an AR ....).

When analyzed objectively, PCC are not logical.  IF they were the logical choice for self-defense ... military and police would be equipped with them.  Think about how much money LE and MIL would save logistically. However, the military places VERY LITTLE importance on handguns.  LE only use them because of the convenience.  Most LE no longer use shotguns for their long gun needs.  Most are now equipped with ... you guessed it ... an AR-15.  If your argument for a PCC/Handgun combo is more "survival hunting" related ... see my comments about choosing a 22LR.

The PCC + Same Caliber Handgun debate pops up in survival forums with surprising regularity.  

Here are a few facts about PCC:

1) PCC fire handgun cartridges which are less effective against human targets than rifle cartridges.  AR-15, AK-47 or SCAR wins.
2) PCC are generally less reliable than high quality military inspired firearms (read up on the use of lever actions by the military).  AR-15, AK-47 or SCAR wins.
3) PCC generally have less "fire power" (capacity and speed of reload) than military inspired firearms. AR-15, AK-47 or SCAR wins.
4) PCC are generally not built to a standard for rugged combat (do you think your Marlin Camp 45 is a rugged as an AK-47?).  PCC are designed and built for the civilian market. AR-15, AK-47 or SCAR wins.
5) Handguns are weaker than a rifle, hold less ammo than a combat inspired rifle, and are more difficult to shoot accurately at distance.  Therefore, handguns only serve two functions: concealed carry and "back up".  Since this is a PCC conversation the concealed carry arguement is moot.  The back up point is very weak.  Ask returning veterans how many handgun ("secondary") mags they carried.  Most I've spoken to carried one in the gun and perhaps one spare.  If you envision needing more ammo - carry more rifle ammo.  Rifle wins.
6) PCC aren't particularly well suited for survival hunting (small game hunting is how people fed themselves throughout history ... large game is hard to preserve in nature).  22LR wins.

Summary:

A) A PCC is inferior to a military inspired rifle for self-defense.
B) A PCC is inferior to a 22 for small game hunting.
C) A handgun's only real purpose is "back up".

Therefore:

Carry a real rifle, and lightweight handgun with a single reload.  The weight savings can be used to carry more rifle ammo.

CASE IN POINT ^^^^

Low capacity.
Concerns about reliability.
Slow reloads.
Far less common ammo than 9mm or 5.56 (which our military uses and most LE use).
Limited range (I'm 90-95% on a human silhouette at 400 yards with my ACOG equipped SCAR).
Slow rate of fire (lever vs semi-auto).
Durability concerns (drive over that revolver and see if it is still timed).
Maintenance concerns (blue vs military finish).

On what planet would this be a better choice than a FN SCAR16 + 9 reloads and Glock 43 + 1 reload.

So ultralight

I still have not heard any compelling reasons

Don't see why warning shots at kids in your yard or anything mentioned here requires a pcc that takes the same mags as your pistol.

For a survival backpack ....

Ruger 10/22 Stainless Take Down with Tech Sights TSR-200 & 10rd Magazine = 4 pounds 11.625ozs
1,100rds Federal 36gr HVHP ammo stored in two 16oz Nalgene Bottles = 8 pounds 3.25ozs
(4) Ruger BX25 25rd Magazines = 6.625oz x 4 = 1 pound 10.5 ounces

Summary:

Ruger 10/22 Stainless Take-Down with AR15 Style Sights
(1) 10rd Mag
(4) 25rd Mags
(1,100rds) Water Proofed Ammo

14 Pounds 9.375 Ounces

ELEVEN HUNDRED ROUNDS OF AMMO

(I just weighed these items on a professional scale).

re: bold - LOL

Lightweight e&e? You bring two guns, and neither has range?  Why not bring one gun with range? Ar15.  223 rounds aren't that heavy.  Compared to 9mm, even.  

Maybe a glock 19 in your pack if you have to ditch your rifle and blend in.   If I'm carrying a rifle b/c I expect gunplay  (.....lmao.....) I'll carry one that can reach out

No go weigh the rest of kit and add it to your 14+lbs...

Same here. If I'm going to the trouble of toting a rifle, it ought to be capable of rifle performance.  Pistols calibers just don't trip my trigger.  OP has a nice setup though.

If you want power I would go with either .357magnum or .44magnum lever action and revolver, or newer school Glock 20 and Mp5 10mm  Of course if you want to be stealth then I'd go Beretta 92FS suppressed and Mp5-SD. Or if you want stealth and power, then I'd go FNP-45 Tactical suppressed and HK UMP suppressed.

That sounds more like a dream sheet than a practical recipe.