all traffic coming in and out. It has character recognition to read license plates. The Sheriff's department is connected to the system so they can flag suspected license plates and dispatch units preemptively.
For example, if there are break-ins overnight in one neighborhood that has them, they can see all the cars that entered and exited that neighborhood at the suspected times. Then if one of those cars enters a different neighborhood, the Sheriff gets a real-time notification and can send a unit to patrol.
LEO apparently love the system because it's so proactive, and nobody has really voiced any privacy concerns about it yet.