Well, if its say $2 per rebuy then its worth playing some crazy hands, going all in etc, and try to double, triple or even quadruple up
( ofc not with crappy hands )
If you mange to do so then you would be way ahead, and then you can play your game.
If you lose then no harm done as you lost only $2 and you can start all over again.
I do rebuy often, especially if i lost at the start of the game. No point if rebuying 30-45min after the kick off, as then every1 else would already have built up their stacks, so it wouldnt do you much.