It doesn't really do anything good for my SA. Quite the opposite, it generally makes it more uncomfortable being around people. If I smoke a lot, I start saying things I really shouldn't. Also encourages circular thought patterns that go so well with ruminative worry.
However, it can be helpful in making me calmer and less anxious in general. So it really depends on quantities/type/who's around/etc. Milder/homegrown, vaporised, by myself has proved to work the best.
Leonard Cohen (Bird on a Wire): I have tried in my own way to be free
Mrs Hudson (BBC Sherlock): Sherlock! The mess you've made!