Normally for a feature film, the music cues are sent to be approved by the director/music supervisor. After the cue is finalized, the composer turns the cue in, usually to the music editor. The music editor will then sync the cue to the film. After the entire score is completed, the music editor will sync all of the music cues to the movie. In the end, the director makes the final call. The composer, music editor, music supervisor can guide/persuade/console the director, but the director calls the shots. This is where communication is vital for the composer and director/post production team. If the composer can explain why he/she wrote the music like that in a non musical way, then perhaps the music would not be chopped or moved around, at least not as much. After all the music is synced, the mixer controls the sound in the entire film. Balancing it out to perfection. This include dialog/music/sound effects.