They literally won't go in to those neighborhoods.

I used to think I was going to be a cop, I joined the explorers and hung out with cops, I went on rice alongs. I spent entire shifts following cops around watching them do cop shit my senior year of high school.

They would spend most of their time doing traffic patrols. The "good" cops hung out in more middle class neighborhoods, the shitheads specifically targeted poorer neighborhoods. No one patrols the affluent areas. When a call comes in they argue about who has to go. A domestic disturbance in the trailer park would get every officer not currently arresting someone out to see what's going on, because they're bored.

They know not to pull certain cars over, to look the other way when certain people are caught drunk or high in public. That's just the extent of the stuff I personally saw.