I've shot & killed a pile of deer with just about everything from a 223 to a 300Rum (including several pistol cartridges, 45 & 50 Smokepoles, archery, and pick-up trucks
). Deer are not that tough & it does not matter if you shoot through or not. If you disturb the vitals they will die.
I have found high shoulder shots with a minimum of a 85gr .243 diameter to be the best stopper. With frangible bullets shrapnel (bullet or shattered bone)will find it's way to the spine to disable, not to mention other physics touched on by RidgeRunner. It doesn't matter if it goes completely "through" or not. Long as it goes at LEAST into the vitals (splashes won't work that great[:-]). I have had many bang/flops with & without passthroughs.
Shots behind the shoulder, generally result in tracking. Passthroughs do help in initial tracking but LOTS of blood later on is actually coming out of the nose/mouth (with lungshot).
Just think. We ALWAYS want the bow to shoot through the deer. If you shoot the boiler room, they always die. Why can't a bullet do the same thing. (I have found frangible bullets are quicker killers here)
I like to have the deer at the spot of impact. I shoot for the shoulder-blades & could care less what the bullet does after it goes 7/8 through the deer. If I want one just to eat, I'll wait for a good shot, whistle, & then shoot the head. You don't have to worry about a passthrough then either!