As a Moon Knight completionist(I'm so goddamn close), I am hunting anything and everything related to the character. I used to keep EVERY copy I could of EVERY book he was involved with but that became staggering. I now am variant hunting so I will have multiple copies of the same book but they'll be price variants, foreign editions, double covers, newsstand copies, artist variants and so forth. So I guess I'm not keeping true multiple copies anymore.
Except Werewolf By Night #32. I keep every copy of that thing I come across.