1. Yes, I'll do it from time to time 2. When I'm climbing and my hands start to hurt/sting I think it feels good to get a cool breath on them. It's also to remove any excess chalk. 3. I climb a little of everything, but most recently bouldering at the gym.
2. Because when I chalk in a way to make sure my whole hand gets covered it usually leaves a lot of excess on my tips, especially if my bag has a decent amount of chalk. Blow or slap the hand on my pants to get rid of the excess, especially on thin face or slab.