I understand that in some countries it is an offence to leave a detachable tow ball in place when driving solo, . In other countries it may be advised that tow balls are removed. But I don't know how or if this policed
To my knowledge it only applies in Italy that the towball must be removed. Apparently it's not for any reason of preventing damage or injury, but that the overall length of the vehicle is affected and no longer agrees with what is stated in the vehicle registration document. For the same reason one has to have one of those red and white striped marker boards on the back of the vehicle if a bicycle rack is attached there. Funny people, those Italians.