Contacts will go to events, they will register for sessions and go to sessions (session checkins).
as part of a follow up email users would want to have dynamic content based on what contacts did at the event.

e.g.
you went to:
session 1 - here's a link to more info
session 2 - here's a link to more info
session 4 - here's a link to more info

This would come in one email and populate dynamically - rather than needing to send an email per session attended which can become too many emails.