In my experience the cops using these systems only care about larger crimes. It's way too noisy to monitor every expired tag, for instance. Not many of these companies (if any) do speed monitoring with LPRs.
But what they will do (and have done) is pull over a vehicle that is registered to a person known to have e.g. an expired/suspended license and use whatever excuse they can find to arrest the driver, even if the driver's license is not expired.
The near-real-time cross-referencing is basically a probable-cause factory, and then its on the person getting pulled over to stand up to all the implied threats of violence that the police can bring to bear.
Prior to tools like this, running a dragnet on e.g. invalid licenses was quite a bit more labor intensive, and so there was a built-in grace allowed to people whose only crime was omission of paperwork.
