To be able to access a log of activity would be helpful, so we could see if they were bulk added or registered/cancelled themselves.

Or if the participants search could return previous participants who had registered and dropped.

Or when there are multiple shifts or days in an event, adding more information to the Automatic 'Participation Update' emails to give more than just Event Name and Participant Name in the email. If it could also include Day/Shift information, then we would know which Day/Shift they dropped from.