Expo Depends on the servo. But I run about -25% expo on nearly everything controlled by a servo except throttle and brake.
Some Servos can be jumpy. I just want expo to smooth them out. Makes adjustments in the air, straight, and sweepers smoother. Making a minor course adjustment when the car is barely touching the ground from a hill requires a gentle touch as well.
Most of our steering inputs are large and blow right through the area expo influences anyway.