According to the Ruff Buff bottle and my personal experience, each increment in sanding, 220 to 320, 320 to 400, 400 to 600, etc. should add about 2 to 4 feet of length to the ball before it starts to hook. Some people need the extra length because of slow ball speed or higher revs.
Applying ruff buff definately changes the surface. It makes the surface less porus. In other words, it might make a 600 grit feel like an 800 grit.