I don't know about anyone else, but for me cannabis tends to increase my focus. At the same time, it does decrease my ability to multi task. It also mellows me out, which increases my ability to tolerate players stalling on the bubble or just playing slow in general.
It was the same thing when I played pool. A lot of the guys at the pool hall wouldn't play with me when I was high. They new that once I "got my eyes right" as they used to call it, they new I was going to be in the zone. They knew they were really no match for me, but they could win a game here or there. But when I "had my eyes right" and really found my focus, it could be demoralizing.