the parking brake is also important when jacking up the car, so it would not roll (that is, augmented by wheel blocks)

when attaching the wheels and torqueing up the bolts, it is best done without any vertical load on the wheel, to ensure proper bolt seating. With the fronts, this is difficult or not possible because the wheel will turn as you tighten it. With the rears, it is possible if you have the parking brake on.

for those with automatic transmissions, it is better to leave your car in Neutral, with the parking brake applied. This is because if it is towed, and done incorrectly, the parking brakes are less expensive than a transmission (!)