Restaurants need more than food for their operations. One necessary service is the delivery of new fry oil and the picking up of the expended product on a regular basis. In addition to a normal schedule, the provider also needs to handle emergency deliveries and needs to change the following day schedule when an emergency has caused schedule disruption.
Many organizations plan their last mile deliveries using routes that do not change very much over time. The customer being visited this Monday is visited by the same person that was there last Monday and will be visited by the same person again next Monday. The case for static routes is that some organizations have a relatively fixed customer base with few changes and that customer base is best served when the same person visits every time an order is delivered.