It really does affect everyone is subtly different ways. I stopped years ago and with about 48 hours of quitting I was astonished that I regained the ability to do mental maths!
I've never understood how it makes some people more productive, and clearer thinking, but it does! Not me though, half a toke and I'd be half asleep.
I know people who study, work, and are totally productive on weed. I wish to god I was like that. I always have to pass on the party cuz I know I will be out of it.