I now see the point of having multiple desktops, but I don't think multiple monitors are necessary. Here's my setup at work:
My home computer has only one CRT monitor. It used to be a 21" model. I decided to try a 19", and found 19" is perfect for me. 21" is just too big.
At work, I've also found that while I have two monitors displaying stuff. I really only use one at a time.
Since Beryl and Compiz/Compiz-Fusion came out, I didn't really see the usefulness of anything like the Desktop cube, wall, expose, all that eyecandy stuff. I sit now with new information. I'm going to flip-flop.
It's been claimed that having a second monitor brings up productity 20% in the average office. With the cube, a person has 4 "monitors". With enough memory, video graphics and such, using the cube is incredibly productive, and using the engery of only one monitor.
So, Compiz-Fusion is green software.