Of course it's not going to HELP your workouts, but next to the common practices of binge drinking, breathing the air in Los Angeles, or whatever, is it going to hurt your gains as much? We start dying from the second we're born. What he probably wants to know is, if he recreationally smokes will it cause a noticeable difference and what would the difference be compared to other unhealthy choices humans make. And how much is too much, and if one quit it altogether would there be a noticeable difference? At least that's what I'd like to know.
P.S. As far as your body's concerned, THC isn't nearly the pain in the ass alcohol is, so I hope none of the people that run down smokers in these threads ever drink.