For me, it's about bringing the writers and readers in wider fandom together. In fandom, we can create these little pockets of experience, where it seems like everyone knows everyone else. You might be involved in only a subsection of your chosen fandom(s), but most likely you know about all of the other factions. The severely polyfannish might know people from all types of places; fandom shift might mean you make whole new sets of fannish friends. But there are still others in fandom you never get to interact with. As soon as you step out of that bubble you've created, you're a lone wolf. And on the one hand, that can be awesome (no expectations!) and on the other, that can be terrifying (no expectations!)
In yuletide, it's really not about the individual, it's about the community. People sign up for it, people write for it, people start to pull their hair out when they realise just exactly the kind of hell they've set themselves up for. There are readers who are eager to dig into the thousands upon thousands of words, and those ready to recommend the thousands and thousands of words that entertained, touched, amused or broke them. There are nervous writers who hope to hell they've written a good story, and most importantly, a good story that was enjoyed by the recipient. It's shared glee, and shared misery, how cool is that?
So, yes, in conclusion; yuletide is love.