Two screens are not better than one (Or how using two screens can lower your productivity).

For years, techies have argued that getting an extra monitor or two for your desktop computer is an especially effective way to increase personal productivity. The logic seemed airtight: Two (or more) computer monitors means more room on your virtual desktop, which means more room to do your work. And more room to work would seem to mean faster work.

 ... But what if we’ve all been duped? What if more monitors and bigger monitors actually detract from, rather than improve, how you work?

From taxprof blog, article here.