I like this theory simply because of how universal it really seems to be. At its core, you can apply the concepts of extrinsic vs intrinsic motivation towards so many things in life outside the classroom. In music learning, there's plenty of extrinsic motivators that fuel learning (earning awards, competition, parent enjoyment) balanced by the intrinsic benefits of improving as a musician. I do feel, however, that there is some difficulty apply this in my content area at times. Music for the musician can skew very heavily towards intrinsic motivations, which can certainly turn away students who don't have as much interest in the subject.