The Calendar Management screen allows you to define Reasons for Instructor absences and Resource bookings. Choosing Instructor absence and Resource booking Reasons when creating those absences or bookings will help facilitate better structured reporting, whereas the Details field can contain further freeform notes.
On the Instructor Absence Reasons tab, you can manage the categories of absences you want to track. For example, you may want to track "Illness" separately from "Vacation" and do aggregate reporting across Instructors.
On the Resource Booking Reasons tab, you can manage the categories of bookings you want to track. For example, you may want to track resources utilized for regular classroom training separately from special events for utilization reporting purposes.