Anecdotally, a friend of mine and myself use marijuana down the former route. Fleshing out ideas, exploring thought. In fact, functional programming "clicked" for me when I was high. It was still there in the morning!
But that doesn't mean every thought is going to be valuable, or even good. If treated that way, I think it can be a good tool. I am thankfully not prone to addiction or reliance.
It reminds me of Carl Sagan's thoughts [0] and especially this quote:
> If I find in the morning a message from myself the night before informing me that there is a world around us which we barely sense, or that we can become one with the universe, or even that certain politicians are desperately frightened men, I may tend to disbelieve; but when I’m high I know about this disbelief. And so I have a tape in which I exhort myself to take such remarks seriously. I say ‘Listen closely, you sonofabitch of the morning! This stuff is real!’
I find it more fascinating to explore thought while on cannabis and that is what I primarily use it for. Instead of saying "dude you're so high" to a far out thought, I try to explore it as far as it will go. Quite enjoyable.
[0] http://marijuana-uses.com/mr-x/