A warehouse operative opens the app on the bus and requests the Friday after next off.
The system shows him his remaining balance, warns that one colleague from his shift is already off that day, and sends the request to his supervisor.
The supervisor sees it that morning on the team calendar alongside the two others already approved, checks the minimum cover for the shift, and approves.
The balance updates, the day appears in the team calendar and in the supervisor's own diary, and the operative gets a confirmation.