Computer screens have gotten bigger and bigger, and I suspect that most users will use the extra screen real estate to keep multiple windows open on their desktop. One for email, one for Twitter, one for PowerPoint, one for Skype. Designers do not have this luxury to spread everything out in front of them, they need a big calm design environment with minimal distraction. My PowerPoint or Keynote screen is always set to the maximum.
I used to work with a laptop in clam shell mode in my office: the laptop is closed, and a big external monitor is used as a display. For copying and pasting, inserting Excel charts in PowerPoint, I was constantly moving windows around. Until yesterday, as I looked at the closed laptop screen.
So now I created a dual monitor screen set up. My slide design application is up full screen on the large monitor, and my laptop screen is used as a collection bin for all kind of bits. It has been a liberation. My 17" laptop actually is big enough for the little side apps that I am running in that screen. Great.
If you are on a Mac, here is how to do it: