Here’s a claim for which I have absolutely no data: I believe I am more productive with a smaller screen/monitor. I have a 13” MacBook Air that I occasionally hook up to a 21-inch external monitor. Sometimes, when I want to read a document I’ll hook up the external monitor so that I can see a whole page at a time. Other times, when I’m using R, I’ll have the graphics window on the external and then the R console and Emacs on the main screen.
But my feeling is that when I’ve got more monitor real estate I’m less productive. I think it’s because I have the freedom to open more windows and to have more things going on. When I’ve got my laptop, I can only really afford to have 1 or 2 windows open. So I’m more focused on whatever I’m supposed to be doing. I also think this is one of the (small) reasons that people like things like the iPad. It’s a single application/single window device.
A quick Google search will find some pretty crazy multiple-monitor setups out there. For some of them you’d think they were head of security at Los Angeles International Airport or something. And most people I know would scoff at the idea of working solely on your laptop while in the office. Partially, it’s an ergonomic issue. But maybe they just need an external monitor that’s 13 inches? I think I have one sitting in my basement somewhere….