According to my dear old dad, who used to work in a garage, and who is still pretty handy with a wrench, tire-kicking was the time-honored way to check out the condition of a car’s suspension, specifically the king pins and king pin bushings. In the good ol’ days, king pin bushings would wear at a fairly reliable and predictable rate. Eventually, the king pins would rattle around in the bushings, indicating that the car had a significant number of miles on it, and that it was time to have the front suspension redone. In order to have a kick reveal the rattle, though, the front end has to be jacked up. A good kick will tell you, roughly, if the miles on the odometer are reasonably representative of the miles indicated by the king pin bushing wear.
You can get the same idea by grabbing the top of the tire and giving it a good shake, but then you get your hands dirty.