My lay theorizing on this: certain types of music (and much of the classical repetoire) helps relax the mind. We spend far too much of our time being grossly overstimulated, and I've found that a great many of the typical stimulations in a Western experience (advertising, technology, popular music, city streets, etc.) simply wear at me. Nature, nonlinear landscapes, classical (or earlier) Western music (there is some awfully annoying non-western music, Indonesian gamelan being very high on the annoyance list for me) help immensely in this regard.
Just as strength training is stimulus for growth that comes during recovery, I suspect music may be part of the downtime which helps the brain and/or emotional / stress aspects of the body recover. Meditation or similar practices might operate similarly.
Total armchair theory here, but it's what I've got.
