I guess I'm too used to the collaboration features of word processors like Google Docs. If I build my own, those go out the window otherwise everyone has to sign up for my word processor and learn my word processor's UX.

For the rest, at least so far, I haven't had the collaboration experience but for word processors I can't go back to local files that can't easily be edited/viewed/commented on by multiple people or myself on every device I own.