Nah man its just to keep the cars potential energy the same as yours ! so when you touch it or get in it you you dont get a static shock, a car works off dc power which doesnt need an earth just a positive and negative ( the Battery ) so you can take it off if you dont want it on the car doesnt make a difference really
I was told that for older cars they had to do it because it had a positive earth which causes rust faster. All new cars have a negative earth. As well as preventing static shocks.