I think it's possibly dangerous to generalise as there are so many variables involved, narcotic strength, individual reactions, if you've built up a tolerance and such.
I've known people in an office environment over the years that seem to function better when they've had a couple of drinks at lunchtime though equally some seem to become useless after just one shandy.
The same is true of weed smokers, some seem to be able to still function quite well after a single spliff, while others are reduced to giggles after just a few drags.
And cocaine use in the City? It's said the City from the late 80's through into the 90's was running on it and I expect parts still do.
There are just so many variables.
What I wouldn't recommend is that anyone under the casual influence of drink or certainly psychoactive drugs should ever be involved with operating power machinery.
From personal experience, musically it's also not a good thing for the rest of a band to have to put up with a member out of their skull when doing live performances or trying to record anything against the clock. Their timing generally goes to shit though certainly for winding down and for creative purposes it can sometimes be fascinating and inspirational, or at least you usually think it is in your Coleridge moment, but productively it's rarely a good idea.