I suppose the fox tail is just an attention grabber to get people to look at your car, and to consider the fact that you even have a car. This falls in with other cheap "bling" like mud guards with a reflector, hanging ground scrap with a reflector, blue dot tail lights. curb feelers, hole punched in the muffler, and other cheap accessories just to "dress it up a little" (akin to making a silk purse out of a sow's ear). Theory is that anything that attracts attention may attract the girls (like a Bower bird), and the more baubles the better. The fox tail is a throw back to the days of hot rods pieced together from a jalopy on a shoestring budget, and reminiscent of the 20's and 30's, but the tradition survived well into the 60's.

In more recent times the fox tail gives the impression that you have a slow car. That might be a useful idea if you have a quick car that only looks slow (a sleeper car), and you might be trying to con a slightly slower car into a drag race for pink slips.