Mine is turning into a PITA. He sneaks up and bites my tangs, carries stuff around and deposits it where he sees fit, and it a nightmare for the snails. Haven't seen any hermit damage except carrying them around a lot. I think they are too small to bother with. I love this guy and have no plans to get rid of him right now and really he's no meaner than my Sohal...
The main thing he does to make me mad is biting the other fish. He seems to do it for fun as he bites them and then takes off really fast and they chase him. All my tangs are big enough to beat him up and I havent seen any injuries to them. He's only about 5" though so could definately become a real problem as he gets bigger.