The visibility of an event can be managed by assigning a user group expression under the tab "Visibility", or by assigning users to a session of the event.
Assigning a user to a session will make the event available to the user in the application, regardless of the user groups defined under the tab "Visibility".
In the case that a user is in the user group expression, the event will remain visible to the user, even when all sessions have past. If the user is not in the user group expression, but assigned, the event will disappear from the user's application once the assigned session has past.