For me i like to work in my tank all the time. To me if I'm not doing stuff in my tank all the time then there is really no point. So fragging just comes as a good way to keep busy. I'm not in the hobby to impress other people, I'm in it to have fun. So I frag.
I also do it to keep the corals away from each other, to me it's just a coral, it will grow back eventually, so there is really no harm done. It also doesn't help that I'm a collector, I keep all My little broken chunks and accidental frags and eventually it gets to be to much! They are certainly not the prettiest frags, but someone might want them
For me a third option is needed! fragging for no real reason!