exponential changes the servo response to stick movement. It will not change the amount of throw of the servo but it will change how the servo moves with the stick. usually the servo moves linearly with the stick movement but with expo you can soften up how much the servo moves when you move the stick near the centers. This is negative expo and is good for flying a plane with high rates and still being controllable. As the stick nears the ends of travel the servo will respond faster until it reaches full travel at the same time the stick reaches full travel. If using pos expo then the servo moves a lot with the initial movement and slows down near the end of stick movement