I think this is an interesting question because I’ve generally found that most people want to put wall-to-wall music in their projects. If done well, this is fine, but if not, it can sometimes hurt more than it helps. Wall-to-wall music can be numbing and make your brain tune out and therefore not take anything in. Not what you would hope for.
There are a few approaches I like to keep in mind when I’m producing audio for longer videos.
Pick a variety of music. Not necessarily different styles, but different tempos, feels and rhythms. If you think your video needs wall-to-wall music to help the visuals along, try to treat different parts of the video in a unique way to give each section a musical identity. For example, if you have graphic sections, have consistent music in each of those sections and don’t use it anywhere else. Try to use some music that has very little or no rhythmic/percussive elements in some of the sections. This will give the listener’s brain a break and also give them a lift when a new upbeat/percussive track kicks in.
If your visuals are good enough and you think they can handle a bit of musical silence, I’d say go for it. A little silence before a big reveal or climax can be very effective and add impact. Think about watching a movie where the audio is quiet and then something big happens on screen. Things go from zero to sixty in the blink of an eye and it’s awesome. It’s a classic film move and is done with regularity because it works.
In summing up, I’d say that you’re really trying to create a nice musical landscape that ebbs and flows and has good dynamics. If you have the same beat going throughout your long video, chances are pretty good that the listener/viewer is going to get bored and tune out.
There are always exceptions, but overall I think these points will help you construct an audio flow that engages your viewer/listener and therefore helps them to enjoy your video a little more.
As always, feel free to send in questions or comments.