If you have an auto tranny, you probably just put the car in P and leave it. Do you notice that the car "twitches" a little when you take your foot off the brake (if you are not standing on a flat surface)? Some cars even rock back and forth for a second or two. I have read that you shouldn't put the car in P without using the hand brake/emergency brake when you park in a hill, because the forces applied to the gearbox. I always use the hand brake when I park, even if it is just a slight incline. (I don't use it in the garage, as the garage floor is perfectly flat). My question is: is it necessary to use the hand brake every time you park, to limit the forces applied to the gearbox, or is it just necessary in steep hills?