Well, since the values of pieces in bughouse chess depends severely on the position type (e.g. a queen is often useless) you may want to stall/not play immediately when you're waiting for a specific piece to complete your strategy in general, not necessarily to win you a piece or gain some specific advantage.
E.g. you may have noticed experienced bughouse players starting with 1.Nf3 followed by Ng5 or Ne5 and sacrificing at f7. Now, when the king takes the knight, you might not reach an immediate advantage, but getting a knight could yield you a nice aggressive position.
Or another example would be waiting to get a pawn very early to disturb your opponents development as early as 2nd or 3rd move, with the goal of attacking, but also getting more space and a psychological advantage.
While we're on that, sometimes if you're playing blitz bughouse casually, chatting etc. you might want to spend some time just to get your opponent off track, since psychology plays a huge role in chess, and therefore in bughouse as well.
However, I would agree with you that on most occasions it is that you see you're getting checkmated in the next move so you let your partner play as long as he can(given that you have more time than your diagonal opponent, of course).
That's pretty much all I can think of, I hope you find this answer useful!