count rebuild is very strong. I'd say it's also a must-have in no +buy games as a way to safely take PPR. if you're down by 3 with 2 provinces left, and get a good turn where you get 8+rebuild = win
Rebuild is weaker in shelter games without the 3 free estates. Or anything where you might be trashing your estates early.
3 is probably excessive, especially in games with terminal + draws.
I'd avoid it in certain alt-vp decks, like a nobles reliant engine, and of course in any engines that draw up all or most of your cards. If you only have 1 non-province left, and it's in your hand, that rebuild is suddenly a 0$ chancellor.
