For me I think I am better mentally when I am creative. If I go to long without my creative outlet then I get crazy. I guess it's probably different for everyone but for me creativity helps keep me sane. It breaks the monotony, distracts me from all the ill's of the world and gives me joy. I believe we are all creative and the more we can use it the better we will be. I do think that many artist's use their art as a cathartic process that helps them release or process emotional grief . That said I don't feel like mental illness creates better or more valid art, I believe that comes from creative passion, creative exploration as well as commitment to the process of making art.
RE: Art and Creativity: The Saga of the Tormented Artist-- Is Suffering Required for Creativity?