There is a requirement to include different information in the email body depending on whether the notification is for the event start or end. Typically, the event start email includes the start time and start values and the event end email also includes the end time, duration, end values and aggregations. The same could be true for other delivery channels.
Currently, the workaround is to create two Notification Rules, one for event start and one for event end, but this is not ideal.