Let's say music is needed for only 43 seconds of film. You have to score it so it is an entity, so it won't bother anyone when it ends so quickly. Or if a song runs 2 minutes and 45 seconds, but the titles run a minute longer, you have to arrange that song so it doesn't get repetitious.
“Madonna is a pro. I don't like her and have no respect for her but- I don't think she should be called a musician or a dancer or whatever you know, but I do have, well I do have respect for her ability to completely manipulate the media and have them work for her.”