Was only marks STOPPED police cars, that are also by the side of the road with someone in them. You (the person using Waze) wouldn't mark a cop parked to eat lunch, or just driving around (how could you mark a car driving around? It's not like Waze is selling GPS tracking magnets... hmm...)
So for someone thinking of robbing a bank or anyone else, all you know is where the police cars are that are in speed traps. At any given moment there are a ton of police cara simply driving all about, that Waze has no indication.
Using Waze does not mean you can speed like crazy, just that you can keep up with traffic without worrying about being singled out for a stop because of the color of your car or yourself.
Waze is also REALLY useful to know when there's traffic ahead (people telling Waze where traffic is beats every other mapping solution I have used) and also hazards like giant potholes, or cars stuck in the road.