i do it sometimes.....depends on the work out and how much i smoke.
if you're really stoned, it'll never be a good work out. you lose your aggression big time
if you take a hit or two, it can definetely help.
bodypart also makes a big difference. i can not smoke and do legs..my lifts suffer and i can't squeeze out that last rep.Ditto for back because of DLing... however for like chest, arms, even shoulders i feel i can get a better mind to muscle connection.