Real Answer: Gravity
If you think compression or transmission holds your car in place, please park it on a 10 percent grade without a parking brake. Let us know how well that works out. Compression in the cylinders leaks out rather quickly, so don’t count on that. Low gear in your xmsn might slow it down, but don’t count on that either. Rolling resistance of the tires might make it hesitate before it heads south. Real Answer #2: Parking brakes hold your car in position, the rest are just obeying gravity.
Explain how parking with your transmission in gear is bad on it?? Just image what power from the engine would do to it.