I watched a few high-level runs of some levels, and the players were able to seemingly cling to a wall, then run/fall down the wall very quickly while still cleaning the entire surface. I've found that if I just land on the wall, then falling takes quite a bit of time. If I dash downards, then I pass right by the surface without cleaning it. So I can either descend quickly or clean the surface.
How do I do both?
For example, shortly after 47 seconds in this video, the guy is able to slide quickly down the wall somehow. I'm not sure how he's managing to do this.