Came across this video interview with Paul Thomas Anderson. Somebody asked him about working with Jonny Greenwood and he spoke about the influence of the Spielberg/Williams collaboration on the use of music in his films (jump to 49:13 in the video):
When I grew up, I was watching Steven Spielberg's movies with John Williams. I was like "Fuck, that's how you do it! Music and what the movie is, they bash together. Not that I'm comparing us at all, but that's what influenced me. That's how it should be. These two things smash together and you're supposed to grab and smash an audience with that stuff. That was my influence, I thought that's how you're supposed to do it. And then I saw what Bernard Herrmann did and Alfred Hitchcock and stuff like that and I was like, that's what you're supposed to do. So that's been my feeling on how music should be in movies.