It's kind of... well, it's the sort of thing that you won't really see the appeal of until you have one. I don't *think* there are ways to lock it, but it's got these different sections; like one for "journal" entries, and one for photos/pictures and one for quotes you like and so forth, and they all show up in your friends' watchlist. And if you like something on your friend's posts, you can reblog it and share it more.
It's a very public sort of thing, which has both its appeal and its drawbacks. But its definitely neat.