Despite popular conceptions promoted by movies and television, many US police departments prefer not to maintain officers in non-patrol bureaus and divisions beyond a certain period of time, such as in the detective bureau, and instead maintain policies that limit service in such divisions to a specified period of time, after which officers must transfer out or return to patrol duties.[citation needed] This is done in part based upon the perception that the most important and essential police work is accomplished on patrol in which officers become acquainted with their beats, prevent crime by their presence, respond to crimes in progress, manage crises, and practice their skills.[citation needed]