If you e-mail a document then you make a copy of it at that instant, but if you send a link then it is updated as the original is updated and the copy is made n

If you e-mail a document then you make a copy of it at that instant, but if you send a link then it is updated as the original is updated and the copy is made not when it's sent but when it's received, which I'd consider to be two very different things. "Sharing" with a group of people like in Facebook (where each one can essentially change the nature of the thing in real time by commenting on it or liking it) is also somewhat distinct from the other two because it makes a send-time copy that can be changed (in limited ways) by people other than you in possibly unpredictable ways.