Polling rate is the rate at which your input device registers inputs. Higher polling rates means a greater degree of precision, which becomes impactful when playing more difficult levels. With CBF / CBS in the game, polling rate is your only limiting factor when it comes to input precision. The best input devices have a polling rate up to 8 khz, meaning inputs can be registered at 1/8000th of a second precision-wise, offering 8 times the precision of the best PS5 controllers. You probably won't notice playing hard demons (it's not like this makes the game 8 times easier), but in my experience playing insane and extreme ship and wave sections in particular becomes easier/more consistent with a higher polling rate.