As for "more margin for error," I think that that is a misleading term too!
Granted, with too small of a bullet, or the wrong type of bullet, your range and target area can be really limited. However, the "big bullet", "I can hit 'em anywhere and he'll drop" theory has been disproven by the fact that larger calibers loose more game! Easier to shoot calibers lead to better accuracy. Deer are not particularly hard to kill, they can be very hard to recover though!A well placed shot from a caliber that you can shoot accurately gives you a much better recovery ratio than any "woundamagnum, drop-em-or-loose-em" caliberwill give you!