Determine who can login, when they can login, install software as a policy, modify registry settings remotely, shut down, restart, etc...
On a network you can manage a remote desktop computer almost as though you were sitting at the machine. A lot more work to do anything like it in a Workgroup.
Most small places with 10-15 machines and not a big budget try to make the Workgroup model work for them, but as it starts to get bigger it becomes more difficult to manage when not on a real network.
