Composing is a stress reliever for me. It takes time, but as the poster above me stated, time that I happily expend because the accomplishment of creating a piece of art is immensely gratifying, even more so when it can be realized via software and technology and shared with others.
While it is mostly a hobby, I actually earned a scholarship during medical school which was specifically for a student entering a neuroscience field that had an interest in music or art and the amount was not trivial. That's the only tangible renumeration I've ever received for my music but honestly, the intangibles (getting helpful feedback and praise from others, the rare case of actually having a piece performed live) is far more satisfying.