Like others, after a round has been chambered and unloaded multiple times, I make sure to shoot that round next time I am at the range with that caliber gun.
This occurs with guns that I might use one ammo for HD and a different ammo to carry with me as my b/u when hunting. Also occurs with my smaller guns that I might use more seasonally during hot (AZ hot!) weather and then unload.
Other than that often chambered round, I look at the gun and rounds in the mags for any dust or dirt accumulation, like when I have carried it for a month or take a spill in the dirt out hunting. Then usually if I am going to clean up the gun and mag, I will fire those rounds. If the ammo and the mag looks clean, then keep on carrying, or if putting that gun away for awhile, ammo back in the box.
Finally, once in a while I just want to reverify POI with SD ammo. So I net out shooting about 1 or 2 mags a year per gun of SD ammo, often more if I am testing a sight change, comparing 1 ammo to another, any parts changes, etc which is sufficient to take care of rotation.