Do you know who had access to your rental or might still have? Even though most apartments management will hand you a new set of keys, what if their former employee still have some key copies? or what if your apartment was not rekeyed for whatever reason? It is absolutely safer to re-key yourself, and you can always hand a key copy to your leasing management for any emergency.
Routinely, we recommend at least once a year. Of course, you can always do it whenever the time is right for you. For instance, if you lost your home keys or noticed they got stolen, or if you need to prevent access from someone.