Xue Sheng
All weight is underside
Maybe Tai Chi would benefit from it. Not monkey-stoned, 'till your eyes are bloodshot. Just a higher level of muscle control. Yes it slows down your reflexes, but I'm not aware of tai chi being about full contact..
apart from that, haven't touched it in 6 years. My inability to control myself under substances left me with enough scars of my soul. Even though alcohol was much worse in that.
Then you don't know real taiji (but that's ok, most don't) and taiji absolutely would not benefit from it. Even with out the MA in taiji it would not benefit from it but it sure would hurt it not to mention be completely contrary to what taiji is.
Marijuana will not enhance martial arts preformance (any more than a shot of whisky will help a rail drag racer just before the race) and if someone beleive it will then they are either fooling themselves or not doing "real" martial arts