According to what I just read on the subject, HDC will slow the vehicle to a preset speed while traversing downhill. It uses the ABS system to help the vehicle maintain the speed. You should have indicators on your dash telling you when it's actively doing something, as opposed to when it's in passive mode (on, but not doing anything). In and of itself, the HDC should not cause your vehicle any additional wear/tear on your vehicle. It only uses the brakes when you need it to. Really, though, the system is there to help you navigate steep terrain, so there's no need to have it on. It may start working when you don't expect it to, which could cause you to have issues with driving. If you don't need it on, it would be my opinion to leave it off. This is probably something like 99+% of the time.