The most useful is being able to easily make changes in an event without having to do so much work. It's also really easy for people who are not super tech-savvy. I have no complaints at all with this software, it does everything that you need it to do. You can't go wrong with RecDyn. We use RDC primarily for our events because of how well it integrates with other aspects of my organization (iCalendar, Eventbrite), but we're using some other features as well. Using RD has saved me hours upon minutes each time I update something about an event or change location information.