When I was about 21, we started working on an album in a studio run by a guy who came really, highly recommended by everyone in the region.
I didn't smoke or drink at the time. And the first day we came into this guy's studio, he walked out in front of the console and pulled out a bong from the cabinet he had there.
He packed the bowl...lit it up right there in front of us all. As he pulled the smoke through, he reached over and flipped switch on the wall, which fired up an exhaust fan directly above his head....where he blew the smoke as he exhaled. Blew it straight out the studio to the outside. Couldn't smell a thing. Crazy.
I got REALLY uncomfortable...but being young and pretty much scared to death of anyone, I kept my mouth shut.
To my astonishment, as the day moved along, it seemed that the more he smoked, the better he got. And most certainly, we were getting free time....so that was cool by me.
And as the weeks went by, I learned to trust the guy so much that even I would encourage him to hit the bong once in a while.
By the end of the project, I was so comfortable with the guy that I didn't even go listen while he mixed it. He knew where we were going with it. And man...his mixes were SO MUCH more than I thought it would be. What a talented guy.
Subsequently...he moved on to Los Angeles in the 90s and engineered/mixed/mastered several platinum and gold albums.
Probably stoned the whole time.
But I'd guess he's the exception....not the standard. Right?