Motivated primarily by a desire for court overtime pay, police officers want arrests on their own terms, ideally without victims, complaints, or unnecessary paperwork. Young officers make more arrests than veteran officers. These officers believe that making arrests is police work. In my squad, the top three officers in arrest totals were three officers with the least experience. An arrest-based culture can exist in a low-drug environment, but without a limitless supply of arrestable criminal offenders, an arrest-based culture cannot make a lot of arrests. Neighborhoods, without public drug dealings will not produce a high number of arrests.
That is from Peter Moskos’s truly excellent Cop in the Hood: My Year Policing Baltimore’s Eastern District. This is one of the two or three best conceptual analyses of "cops and robbers" I have read. It is mandatory reading for all fans of The Wire and recommended for everyone else.