I use it when going up or down 長命斜 or 多彎的路
幾好用架 before that I only used brake when going downslope and both passengers and driver are not comfortable. But when using +/- can "gradually" slow down your car instead of "chok" 又無咁傷個 brake,亦唔駛用到 S 波 (S波力度最大Ma but if 對付長命斜而斜度又不太大的,上落斜時會很choke...) ,況且下下用S波亦waste gas d