I've written about this before but don't want to go look it up - in fact the key discussion for me was probably between JLNobody and myself on the old abuzz forum. I might define "play" as a little different than present common assumptions, seeing exploration as almost an equation with play..
but, anyway, to me it's a key part of art and design and the prime reason I'm interested in art and design process. I changed my life towards art and design while I was still working in medical labs because of the satisfaction of the play component. I'll grant some med research involves play, but I wasn't personally in that stratosphere, though my bosses were.
Of course I also often like the visual or aural results of my and others' "play", so the process and the results work as a pair to me... well, they work as a pair whether or not I think the results are great at the time.