Blade- First hand knowledge of a shooter who used it for exactly that, and with marked success (unfortunately as naive as I am, I only learned about it well after the fact). Ended a 6 year + friendship because of it.
I took your advice (about googling it), and googled "marijuana performance enhancing drug", and the first result on google is, "Yes, Marijuana Can Be a Performance Enhancing Drug".
The primary benefit would be chilling you out and lowering your sense of apprehension or worry.
Obviously you'd have to experiment and find the right "dosage", but once you did, it would DEFINITELY give you an unfair advantage.