The City Government I talked about in that earlier post had a severe absentee problem, even though everyone (in a site that had thousands of people working there!) had to punch a time card. The time card measured things in terms of tenths of an hour, or 6 minutes. Management decided that since people had to punch in and out, even for lunch, and if they were late, they could dock their vacation in tenth of an hour increments.
This meant that people could take vacation in 6 minute increments. So they did. Several times a day.
Your boss wants you to do something at 11:15, and you've booked vacation from 11:12 to 11:18? You could look him in the eye and say, "No, I'm on vacation." And there wasn't much they could do about it. Imagine thousands doing this everyday, several times a day, at random times.
Management decided on living with the absenteeism.