Not just an excuse for a pull - also an excuse for your insurers to void your policy when you need them most... after you've been involved in an accident.
Just takes a harsh loss adjuster to spot them, note that they're illegal (which in turn contravenes the T&Cs of your policy) and he'll surmise that you've potentially affected the handling of the car which possibly contributed to the accident - so you'll be on your own.
Not too bad if it's a minor scrape with someone in a Ford Fiesta and you have to cough up a few hundred quid, not quite so clever if it's a collision with a Ferrari or there are injuries involved.... then you could be looking at hundreds of thousands or more!