They're useful. How much you trust them and how much the Wardens can see of what you're using them for is up to you.
There's a map, there's a help file, the 'welcome message' is permanently stored in there. They translate between different languages, both spoken like this, and if you happen to be reading a book in a foreign alphabet.
I wouldn't go around too much without mine unless I'm looking to really hide and I have people around who speak my language.