Just wanted to say hi. --Joey
Let me answer this in three parts.
First, why use a wiki hosting service at all? Convenience. We take care of all the details of getting everything to work, fixing things when they break, and providing sufficient resources to keep everything running smoothly.
Second, why pay for wiki hosting? Ads and accountability. There are some wiki hosting services that don't require you to pay, but they tend to put ads on your wiki instead. Also, since you don't have a business relationship with them, they're mostly free to do anything to your site. If you pay for hosting, you have more control.
Third, why pay us rather someone else? Freedom. We are committed to providing a hosting solution that respects your freedom more than ours. That's why we give you access to the full version control history of your wiki, etc. There are some restrictions on what you can do, dictated mostly by security needs, but we keep them as minimal as we can.