You don't need one until you need one, Islay. Not until the person in front of you reverses into you and claims you ran into the back of them. I bought mine after 2 incidents. One where a teenager suddenly ran into the road in front of me in Germany; I stopped but might not have but would have been able to prove I was within the speed limit etc. The second where the police in Austria pulled me in accusing me of knocking a moped rider off and not stopping; I was able to convince them that I'd seen the rider sitting by the roadside as I passed but still suffered an hour's delay.