I believe what it refers to is when you have a "session expired" page come up that requires you to use your password to login. The sitter can enter their password for the sat account, and it'll "login" through there. However, because players can play multiple worlds, it in no way refers to the ability to put in your password for the sat account and login to that world, because it would also give you access to their other worlds that you're not sitting on.
However, I would like to see a fix for this myself: maybe something along the lines of when you're sitting an account, you can login using your password but it'll only give you the option to login to the specific world you're sitting on. As for the mobile app, I don't see a way around the issue, because unless the mobile app opens up a new set of options (ie. overviews, tribe forum, etc.) and lets you switch between them (much as a web browser would) I can't imagine a way to make it all work.
