i usually work on a computer and i usually wear contacts to work. when i'm stoned and wearing contacts i just cannot keep my eyes in focus at the typical 2-3 feet from the screen, so that's out for me. also i deal with very angry people with tech issues and that's just a buzzkill.
i used to work secondaries in a machine shop and being stoned wasn't a good idea there, either. it was way too easy to zone out and that's when things get bloody.