The best thing about this software was that it allowed us to keep track of all our event registrations in one place so we could easily see what events have been confirmed vs not yet! I would say the biggest drawback with this application has more to do with how quickly things change (i.e., new information comes out) as opposed to any specific features or functionality within their product itself.
We used them primarily when planning large conferences/events at my university. As soon as an attendee registered they were added into the database which made tracking down those who hadn't come through registration much easier than trying to find someone's email address online.