On a long down hill if you use your brakes too much you risk brake fade and glazing. With electric you need regen or if you have no more room in the battery then you need resistive braking. With an ICE you need to be able to lock into a lower gear. Standard behavior eith a cvt is to gear as high as possible when not under load so you need "manual mode" and the fake gears to pick a ratio with good resistence.