Roster does not currently log anything in the Sakai event log. The event log is useful both for site statistics (user activity within site, e.g. as reported by the UFP SiteStats tool), and for research purposes when investigating how users have used Sakai, which in turn is important for informing further development.
Roster should post events to the Sakai log (roster.*) for each meaningful user action, e.g.
roster.view = User views the roster
roster.view.profile = User views a user profile
The REF field should include the site id (context) and where the user views a profile, the target user's eid.