i dont know if its true but i would think driving with it off you would get worse gas mileage in town because the engine stretches out the points where it would normally shift (to lower rpms in a higher gear) letting you hit a higher rpm range which i would take to mean burning more gas. i definitely notice a power difference driving with it off especially on those borderline points where it usually shifts - instead of punching it and waiting till the car shifts into a higher gear at lower rpms, you are already at higher rpms and just take off. i dont know if that was true or technical but thats what ive seemed to notice, correct me if im wrong