You need multiple independent machines connected over a network - but it's great if say you have one machine dedicated to text based stuff, one to rendering, or lab work -- whatever it may be.
Any situation where you have more than one computer and want to be able to control them all with one mouse and keyboard.
This setup is better than remote desktop because the computers are stand alone, and suffer less resource limitations.
In my shared office we recently installed an old all in one computer on the wall. We didn't want to put windows 8 on it so we used linux instead (ubuntu mint).
Setting up synergy we found it was not direct as to how to get multiple mice and keyboards to control one screen. We wanted to be able to pull up projects to show one another as simply as possible.
The easiest fix is to open TWO instances of synergy on the client machine
Change the port the client listens on,
Change the port the server communicates with (so that they're both unique)
and supply the server's unique IP address for both.
We had to do a little fiddling to get the monitor setup right - I don't think we could all come in from the same side - so one employee is coming in from the right, another from the left and one from below.
It works exactly as expected, super cool!
Remember to open the necessary ports on your workstation firewall!