Mountview cops have been known to pull drivers over who are going too slow because they suspect they are drunk drivers who are being extra careful to avoid being pulled over by the cops. If you are in a bar late at night in Mountview someone will often warn you don't drive too slow when you drive home.
And for those of you who don't get out of Mountain View very often, the police do this everywhere in the world.
They'll often pull you over for speeding with the intent letting you off with a warning if you don't qualify for a for a larger infraction (drinking, drugs, warrants).
It lets you know that they're out there, doesn't alienate the public as much as giving frivolous speeding tickets does, and gives them an opportunity to catch people that are doing things more egregious than speeding.