Old Joke, is old and more ironic then practical
+The landlord installed it many years ago, before the 24-hour store signed the lease.
+Sometimes, when the clerks work alone, they also need to go to the bathroom.
+So that you can lock down in emergencies, such as tornado warnings, or lock down situations or when they're doing construction.
+They can lock up on holidays such as New Years Day and Christmas.
+For occasional, temporary down time such as inventory control.