If you obey the posted speed limit and have your vehicles lights in good working order, your chances of getting pulled over for a traffic violation just got cut dramatically.
Note the keyword there: chances. It's not about whether you are actually violating the traffic law or not, but how to reduce your chance of being accused - rightly or wrongly - of violating it. And watching your speed is indeed a good strategy of risk reduction.
The problem is a cop can basically find a reason to pull you over if he wants to just by following you down the road long enough. And if he doesn't see anything immediate, he can simply make one up. He can simply say you were "swerving" or "accelerating too quickly" or changed lanes "aggressively" and on go the flashers.
If he's a corrupt cop he may even rig a speeding ticket against you by toying with his radar gun's calibration, or taking a false ping off another car, or simply saying that he "matched" your vehicle speed with no way to independently verify if he's telling the truth.
Since cops are human they can and do lie - especially if there's monetary reward involved. Some cops are indeed more honest than others, but there are so many of them out there that it's a statistical certainty the average motorist will encounter a dishonest one at some point in his lifetime. And when that happens he will have money stolen from him.
Since all traffic tickets in most states are discretionary, anyway, his post is meaningless anyway...