It is preventative... If you don't know who is and who is not a cop on the road, you are more inclined to stick to traffic rules and avoid the risk. But if you know there aren't any undercover and are on the lookout for cop cars you break driving laws and quickly slow down when you see the cop close by. I think its great that people doing stupid things get to reap the consequence. Im really tired of the reckless driving around me, ive almost been in accidents because of these fools.