bad writers use because they aren't clever enough to write something a different way ... usually. As you pointed out, sometimes they are essential. Often, they really aren't. You see it in trilogies a lot too ... the first book is clever, creative writing. Then they run out of ideas and the later books get increasingly more filled with "stuff" because the author is running out of ideas.

Really clever writing, and really hard to do I know, is to craft emotional lyrics/stories/scripts without those crutches.