My face tends to be pretty expressive if I don't think about it, so if I'm going into a situation where I don't feel comfortable putting my thoughts or feelings out there, I might look in the mirror to work on my expression/gain composure. And yes, I think it helps... it puts me in the more objective state of mind I'm needing to be in. Other than that, I try not to spend too much time in the mirror... that just breeds self consciousness.