When you approve time off for an employee, you want to make sure that you don't end up unexpectedly short-staffed.
The more managers who can approve time off, the higher the risk of not having enough employees available.
Usually, the problem arises during holidays, like Easter, Summer and Christmas, when you want to be sure that you have a minimum of - let's say - 5 hostesses to take turns covering the shifts during any given period of time.
Go to Settings > Absence, Overtime, Vacation > Limits > Create
to set the maximum number of employees who are allowed vacation and/or time off at the same time.
You can filter the limit by departments, employee groups and employee types.
Remember to save.