Several people have commented that you might think you're doing some really great stuff but then when you're not under the influence, realize that it was rubbish. If you play music at least partially for your own enjoyment, I still think that's something. I think also that it's possible it will enhance you're creativity, or perhaps lessen the degree to which already-learned precepts / practices / habits, etc., guide your behavior and that could lead to some cool stuff and on analysis, insights...or it might not. Echo-ing what Faith said, if you're like me, you might not remember what you did very well (high or not). If I stumble onto something interesting while playing, I'll try to write it down as best I can and probably record it on my phone as well (since I am terrible about accurately transcribing or interpreting rhythm notation). Also, back in the day when I was enjoying weed somewhat routinely, it seemed like the creative thinking that it inspired was mostly for the first year or so, after which that effect gave way to a general lethargy and the feeling that it was affecting me in negative ways even when I wasn't high. YMMV as they say.