It's the same with boating in certain areas. USCG, Marine Police, Harbormaster, Game Warden ... all trying to find the same guy with a box of expired flares. Except in their case, they can just board you. No suspicion or PC needed. Sounds like easy money to me.

Driving to work today I saw a county car sitting in someone's front yard. Guess he asked permission.

I just want to point out what should be somewhat obvious. The people going through the checkpoint will generally all be okay; as in sober enough. In other countries where I have lived like Canada and Germany it's pretty obvious the people who go through the checkpoint isn't what they're interested in. Roll by with your window down and say "Hi" and they'll wave you through. If you're with your trashed friends in a taxicab you get a thumbs-up. One of the things in those countries is that for the most part, normal peoples' relationships with the police in those countries are a great deal less adversarial because the police get a lot less slack for untoward behavior by the courts.

It's the people that take quick turns off the road from the checkpoint that get stopped by units, and there is RAS in terms of "why did you suddenly turn here when you saw the checkpoint?"

Not arresting anyone at a checkpoint is a measure of success - the people arrested for DUI on the side streets don't get counted, and the deterrent worked.