I agree 110% with that. I always hate to think of someone practicing on a junk panel that just happened to have hard or thick paint and then hitting a car with soft/thin paint and BAM. Practicing on a painted bumper piece is a very good idea, and that would be an area where a smaller wool pad would really pay for itself by generating less heat.
I don't need to do a lot of rotary work, but every time I pick that guy up I'm respectful of what it has the potential to do, both good and bad. When you loose that respect, become distracted, or too casual (think you mastered it after one hood), then that's when something is more than likely gonna happen.
Using a rotary isn't that hard, after all it isn't brain surgery, but it does take practice, knowledge, and skill to be come really proficient.