[MrFlippant]

Sounds more like a scare tactic so that people don't remove them and annoy the neighbors trying to listen to the wireless. ;-)

The big secret is that they do NOT effect the power the motor gets. Analog racers, to this day, remove those in the mistaken impression that they'll gain any kind of voltage or power by doing so. Fortunately, removing them doesn't hurt anything these days.

As Leo pointed out, though, if it's a digital car, you'd be well advised to leave them on both the guide and motor, but especially the motor. Some systems even need extra ones added.