One explanation that I have heard was that it was to rock the wheels to check for a bad tie rod or bearings.
I can testify that you can hear/feel a really bad wheel bearing or rod bearing by kicking the tires hard enough, but it’s absolutely not a reliable or repeatable thing to do. And if it gets bad enough to hear by kicking the tires, then the suspension is probably “24-carat fucked” on that wheel.
I can also testify that once I discovered a brake caliper that had not been installed properly after a brake job. I was kicking the tires of a friend’s car as a joke, and noticed a strange rattle. Turned out he hadn’t installed the anti-chatter spacers properly (not any real danger on this car, since they typically rusted and fell off, but it sure amazed her that I could detect it it with my innate car wisdom…).
The Prince: “Did you kill Jahamaraj Jah?”
Lady: “Yes.”
The Prince: “My Gods! Why?”
Lady: “His existence offended me.”