I wonder how much data sharing we would actually do if this did exist. For example, your Facebook friends list is not your Twitter follows, nor your YouTube sub

I wonder how much data sharing we would actually do if this did exist. For example, your Facebook friends list is not your Twitter follows, nor your YouTube subscribees, nor your phone contact list, etc. There's some overlap but essentially they're different lists. Isn't a lot of stuff like that? It still would be nice to have control and visibility of all that data automatically.