This thread is a good reminder to consider ammo a consumable.
As an EDC/CCW kind of guy, my best practice to to rotate my ammo on a yearly basi during the week of my birthday. RDS sight batteries get replaced that week as well.
If I was a professional gun carrier, I would be rotating my duty ammo on a quarterly basis even if it meant going into my own pocket.
Having said that, in many depts and at many ranges that serve in a regional capacity, if you are a shooter, the range staff will take care of you on a rotational basis that may exceed that agency wide policy/practice i.e. yearly ammo rotation during the annual qual/in service.
Finally, it is the custom/practice of many of my FED LEO partners who regularly work in rural areas to have "extra" ammo with them in the car for all manner of ad hoc training/instructional purposes and/or to have some the next time they go to an area when a need/want/desire becomes apparent.