Prevent clients from seeing each other
You may have just scored a sweet deal with a big client. Time to lock them down so your other clients don't get jealous!
Clients see you but not each other
Clients can provide lightning fast feedback without worrying about sending to the wrong "Doug"
Turn departments or teams into squads
Put all of your designers, developers, or marketers on a separate team so they don't have to see the rest of the company in their friend's list.
Section off by floors, locations, or departments
The entire San Fransico office probably doesn't need to talk to Copenhagen daily. Best to give the two cities their own private team.