There is really one major “pro” associated with assigning a particular officer to a particular beat. Other “pros” come about as a result of the main “pro.” The main pro associated with this is that the officer gets to patrol the same beat over and over and becomes familiar with that area.
This, in itself, does not do the police department or the people of the area any good. However, this familiarity does lead to positive results. First, the police officer’s familiarity with the area means that he or she is going to be more effective at preventing crime. The officer will come to know which people “belong” where and at what times. The officer will have a much easier time determining when a particular person might be about to commit a crime.
Second, the people of the area will become familiar with the officer and might help to prevent crime and to solve crimes that have occurred. If the officer becomes a familiar (and well-liked) figure in a given area, people may tell the officer what they have heard about certain things. They might tell the officer about a crime that they know is being planned. They might tell the officer about suspicious happenings that can be investigated. When a crime is committed, they might give information about that crime.
In these ways, assigning an officer to a given beat can reduce crime by making the officer and the people of the area familiar and comfortable with one another.