Weed is unlikely to have a massive impact on your play one way or another unless you get yourself like totally stoned in which case your out of it and pay worse.
i suppose maybe some placebo effect might happen if you truly believe this helps you.
also if you suffer from anxiety or fear it might help mellow you out so you can just go for it when you need to and not let emotions affect you in the same way.
after suffering a few bad beats from terrible players in a tournament i nearly won a lot of money in it might stop me doing this.