In short, if you and your friends use Who's Talking and you're on the same channel on TeamSpeak, you can see each other's positions rendered directly into the game. This makes it easy for you to keep track of each other in crowded situations.
By default, your own icon is shown to others only when you talk on TeamSpeak. But you can change that to either Always or Never. If you pick Never, the only time your icon is shown is when you press a customizable hotkey. Picking Always is ideal if you are in a small group and you want to let your friends always know where you are.
To make it easy to distinguish different players, every user can pick their own icon and a color for it. And if the profession icons we ship with the software aren't enough, you can easily pick icons from your own computer.