From W3C Wiki
In some sense, all naming is really local: each person, or more generally, each agent can use whatever names it likes for things. But it's sorta boring and costly to start every conversation ala "see that guy? I call him Jark. He calls his dog Rex. Oh, you call that dog Spot? OK, I'll keep that in mind..."
A group of people that have some things in common to talk about will establish shared vocabulary, i.e. a shared set of bindings between names and things. This shared vocabulary has a tangible value: it reduces the cost of communication in the group.
Meanwhile, it creates a cost to join the group. If you ever didn't get the inside joke that everybody else is laughing at, you've experienced it first hand. This results in a natural boundary around a group with a common vocabulary.
Communication between two such groups looks a lot like communication between two individual agents that don't share a vocabulary: "You see that thing at the back of the car? You know, the trunk... well, those crazy Brits call it the boot."
perhaps a bit about fractal social networks here... cf Fractal web, fractal society, TimBL, ~1999
Electronic mail was first deployed in local area networks. Within
these LANs, there was a shared vocabulary of mailbox names. As email
was deployed at greater scale, these networks were connected together,
and the "bang path" syntax for cross-network mailbox addressing
mailgate!utexas!cs!bob might get you to Bob's
mailbox via your own email gateway to the outside world, which
knows the University of Texas network by the name
within that network,
cs was a server for Bob's
mailbox. This worked, at first, but the cost of finding a path
to each person you wanted to send email drove up the value
of well-known mail relays, at first, and eventually motivated
a pretty complete replacement of bang paths by global
mailbox@domain addresses, where DNS establishes
a global vocabulary of domain and hostnames.
Finally, you could put one address on your business card and give it to anybody in the world, and they could send you email. Not only that, they could give it to any third party, and so on, and it would still work.
This ability to use common identifiers across communities is what motivates global naming in WebArchitecture.
RFC:2826 "IAB Technical Comment on the Unique DNS Root"
more on the risks associated with sharing, policies for who gets to introduce new bindings.