I play chess high often, and i would say it barelly matters in terms of strenght of playing, and there's even the chance it can help you. For instance, thought processes are certainly slowed down, but the ability cannabis has to relax and help someone concentrate on creative activities, can in fact change my own gameplay from tactical to more positional for example. If you get nervous with OTB games like i do, it might really calm you down and allow you to think straight and fearless.
Aside from this, i know plenty of chess players, even titled masters, that do smoke their own joint probably everyday and still handle to be grandmasters.
wonder what poker players do to help them perform at their peak.