Every operation has coverage. Most have it in the form of whoever is free that morning.
Why it matters
Absence is not an exception; it is a certainty spread across the year — holiday, illness, training, turnover. The difference between operations is whether the answer was decided in advance or improvised at seven in the morning.
Improvised coverage costs twice. The route is driven by someone who does not know it, so it runs long and the work is weaker. And the accounts lose their continuity, which is the thing that was keeping them.
How you notice it slipping
Coverage falls to the same two helpful people every time, which is how helpful people end up with the worst weeks. Nobody can say who covers a given lane without asking. Planned absences surprise dispatch, because the calendar and the schedule are not the same system.
What to do
Name a backup per lane, not per person, and prefer a neighbour — somebody whose own territory touches it, so the coverage drive is short. Then make planned absence visible to the planner far enough ahead that the work can be redistributed rather than absorbed.