Why cop cars at intersections?

In grad hospital this one intersection has been being worked on for months now. Everyday they block off the intersection with a cop car then leave at the end of the day. Why does it need to be a cop car? Why does a cop have to be in it?! I walked by today and the officer was asleep. Now I know being a police officer is a hard job and they get a wittle sleepy after lunch, but wouldn’t it be just as effective to drop off a car with no officer? Wouldn’t it be just as effective to place a barrier that isn’t a car? Why such waste?

My assumption is our city is just so safe there really isn’t much else for the cops to do.