If the position is even and one player is keen to exchange minor pieces, they will get their way eventually. The goal of the player who would prefer not to exchange is to permit the exchange only with the best compensation on offer.
In practice, that's not particularly relevant for me though. At the sort of ratings I play at, it's usually trivial to exchange a Knight for an opponent's Bishop while doubling their pawn, for instance. I like to think it makes a difference but my matches are decided on blunders, which have 10x the impact.
Is it easier to take away the bishop pair from your opponent by capturing one of theirs or to keep the bishop pair by preventing them from capturing yours?