Let's say that you have supplied, well recorded tracks to mix. So you listen and imagine the build-up (crescendo) in your mind. Surely there is there just one build up? - somewhere towards the end of the song.
The problem I've had (and still do) is to decide where that crescendo should be.
If I'm the one who wrote the song, then I can re-arrange it. If I'm in a position as the producer, then I could suggest to the talent to re-arrange it.
I've mixed a few songs where I've no doubt gone too far - too early, and therefore leaving the last part of the song ultimately very very very . . . boring. . . .