You didnt get the point. The game will stress the cpu as much as it is supposed to, to function seamlessly on whatever settings you choose. Maybe lower settings will put less stress than higher settings. But there are additional processes which runs in the background, which are not related to the game itself, but which adds extra burden to the cpu while gaming. Some of these processes might not be absolutely necessary while gaming like windows updates. What a game optimizer does is stop these processes which are not necessary during gaming so that the cpu can accommodate more input from the game itself and give some leverage to the cpu in that sense.