Think of this as soft handlebar grips for your knees. The tacky, lumpy surface lets you grip the tank with your knees much better than the painted surface you spent ages polishing. Why grip the tank with your knees?
The long answer is four days at the California Superbike School. The short answer is to brace yourself against the bike to help keep it stable during cornering and take weight off your arms under braking. It really works and I wouldn’t race without it. StompGrip is also one of those products that works for you no matter what your riding level.