I find the question a bit interesting, actually. When I think of organized rides, I think of rides that I might have with one of the cycling groups I belong to; not so much a charity event per se. Guess everyone's interpretation is a bit different.

That said, I think the general alure is often either charity events or organized rides that are "just for fun" tend to give you more venues upon which to explore areas with which you're unfamiliar. If you've got a Garmin and know how to search for courses that others have created and/or make your own and put them on your device, then in theory you can do this yourself. But you miss the colleagial aspect of riding with others.

Also, whether you're talking an event or just a club ride, as a rule, people often push themselves more on these rides, giving them a better idea of what they're capable of.