Frangible ammo is primarily for training. Shooting steel targets at close range is what it is specifically for. I have not shot frangible rifle ammo, but I have shot a shit-load of frangible pistol ammo. The ammo turns to dust when it hits objects greater than a certain hardness. Anything softer, and it stays intact. This allows one to shoot at reactive steel steel targets without worry of bullet back-splatter or ricocheting bullet jackets. The pistol rounds I shot were made of crushed copper. All around the targets was this brown copper dust.
Anyway, the stuff is expensive, and unless you need it for certain range requirements, there is no advantage over regular ammo. One other thing, frangible ammo is fairly un-common on the open market, so, if you plan on using this stuff, pick some up for later.