Two cautionary tales come to mind. We had an Instructor hit hard in the hand by an improperly installed fire extinguisher once. It didn’t break any bones but the top of his hand was blue for a couple of weeks. The other was a student I was teaching. At the end of the back straight a tennis ball came out from under his seat and lodged under his brake pedal. He learned to enter corner eight at speed and I learned how to crush an armrest while screaming “brakes”!
Since those good old days our criteria has become a little less casual, but it’s all in the interest of your safety.