Few years ago there was a woman whose van rolled into a lake. She had put it in park, not knowing the parking gear was either fragile from misuse or already broken. She wound up burying her three kids.
I grew up in a town consisting of a bunch of short but steep hills. I knew one family that would break the parking gear on every car they owned within three years. They would park on the hill out front, put it in Park, and let off the brake, letting that tiny gear take all the wieght of the vehicle with passengers. It would hit so violently it would bounce back several inches. Took them four or five cars before they figured out what was going on.
The parking lever serves the same purpose as leaving a manual in first gear: the brakes should hold well enough to keep pressure off the tranny. If they don't then it's there as a safety measure.