This document describes what happens after an event is cancelled using the Scheduling Assistant.
In the appointment cancellation workflow, your actions told the Scheduling Assistant with whom and what time the event was. The Scheduling Assistant uses that information to cancel the event in the calendar server and clean up any event remnants.
The reason field is optional, however if populated allows the Schedule Visitor to relay a message about why they couldn't attend. This information is sent in an email to both parties describing that the event was cancelled and including this reason.
Like for event creation, EventListeners can be implemented to respond and perform custom logic when an event is cancelled.