The Absence report shows the absences that were entered into each time card per person for a time period. This one gives the employer a view into an employee's habits and possibly points out an employee abusing the system. It can also be used to help keep track of vacation.
The Absentee report shows employees who did not punch in on a day their schedule in their group says they were scheduled to work. This can be used as a way to look at gaps in positions for today like at a school or it can be used to identify employees who fail to show up for work.
Both reports are most useful for managers who may not see every employee every day or who are looking at trends over time.