If you come on my property, I've got you from the second that you enter on. There's little lasers... my TVs come on in my room and fall just right on you. So, there's no way to sneak up on me. And I've got a loud dog.
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.

