WHY? For Fun Ok maybe. But well placed shots are better. Than a whole bunch of shots that don't hit their mark. Thats why I hunt with single shots and my BP guns alot . You have to make the shot count.
I've never used bump firing for hunting purposes, nor would I ever, or ever recommend it. It would be unethical. Yes, well placed shots are better, but sometimes it is fun to send a lot of lead down range at a target. I don't care if a majority of the bullets miss their mark. It's for fun, and I almost never do it (mainly because I can't afford to). If money was no object, I would probably own a full auto lower receiver and I would be doing a lot of mag dumps for the hell of it.
Rapid fire can be fun, whether you are bump firing, or just plinking at targets as fast as you can. It really doesn't benefit you as far as hunting, but it's all for fun. I'll never forgot when I purchased my first AR (I've got 4 now. They are addicting!). The first thing my dad said when I stopped over and showed it to him, was "What the hell do you need that thing for?" Needless to say, after he blasted through a few 30 round mags filled with cheap ammo, he said he completely understood. I then showed him the accuracy potential with some of my handloads. He couldn't believe it when I turned in a couple of 1/2" groups. When ever my shooting buddies and I stop out to the folks' house to shoot, my dad is one of the first ones asking for an AR.