Long before the first talkie, producers were including suggested musical scores for orchestras to play during their blockbusters. Hollywood PR flacks would also commission pop songs just to remind people of the names of their pictures. Maybe we have made some progress. The point is, music and the movies have always gone together. And with today's wide selection of library music, there's no reason your QuickTime classic can't have as rich a score as Star Wars .
Music can add the right seriousness, importance, or excitement to a presentation.
It can tie a video together when the pictures don't match, or delineate sections when the topic changes. Many films and tv series are scored by people who can't play a note. The ability to look at a script or roughcut, tell just what music is needed, and describe it properly are more important than keyboard chops. In fact, the Music Director on a feature often hires someone else to write the themes, and relies on library music as well. It's more important that you understand the emotional flow of your message, and have some way to get just the right music.