This could be annoying, but it could also be quite useful under some circumstances (especially if it's a well-done soundtrack). When the music turns suspenseful you'd know that there's danger nearby, and it could help out with circumstances where you're trying to set the mood. Romantic music when you're out on a date, uplifting or dramatic music when making a speech, etc.

Also, movies don't usually have background music playing _all_ the time, just in significant moments. That will help preserve sanity somewhat.

Only if it was composed by John Williams or Hans Zimmer