If you have your foot placement and technique down it really doesn't make much difference. I think most people do it to stay close to the wall. By touching the wall on the way up it gives you a mental note as to how high you are, how fast you're going, and whether you'll make it or not. It's just kind of a reflex thing. For instance...



That's a pic of me doing a pretty high wall climb in Philly. I'm going straight up the wall and I'm using my hand as balance and all the other things I said. Make sense?

          When I kick up, I need to keep my hands at least in a similar position of touching the wall so that my body's in a good form to move upward.  It keeps my hips and head parallel to the wall on the way up.  I really do wish that I didn't have to hold the wall, it makes it hard to grab the ledge, but it's somehow necessary for me to move up with my hands in that position.

Yeah, not really a grip/boost issue. More just a guide. I think most people do this without even knowing it. On the other hand (or foot, for that matter) though, a second step will help. With the right technique it'll add another 6" to your wall run. A lot of people only take one step because it feels more natural that way. So, in most cases you have to consciously make yourself take that second step. Just one more way to fine tune your wall runs and milk them for all they're worth.