There could be any number of reasons one might have the need to know p.o.i. changes between a suppressed and non-suppressed rifle. In my case, I've got a new gun bearer type of sling attachment for carrying the Predator on my back pack, this hunting season. The butt of the rifle will be down, below and behind my hip, the scoped area of the rifle will ride under my armpit and the barrel will come up beside my head on my strong carry side.
I'm just not sure I want the can on the end of the barrel while I'm humping around through the hills. First, if I take a fall, I could possibly bend or damage the barrel, the threading or the can, itself. Secondly, I'm not sure I need the can impeding my vision off to that side of my field of view. Right now, I plan to do my walking & hiking without the can mounted and thread it on when I sit on stand, occasionally. Thus, the need to know what my p.o.i. will be in either situation. It may prove to be more of a hassle than its worth...just not sure which will work better at this point.
I'll know more after I try the system in the field a few weeks from now during combined deer & elk, 3rd rifle season.