As an admin, I'm frequently asked to add users to the system. I generally will search for a "like" user already in the system and check to see what groups/teams/access level the current user is assigned to, and set up my new user in a similar way.
I have "New from Selected Person" available to me from the People/People tab, but I don't necessarily want to set up a filter to allow me to see only the subset of users I want to see. It would be wonderful for admin users to have the option to create a new user from an existing user's details tab.