Most folks have probably already figured out for themselves that having to use a painfully small display with a low resolution impedes their productivity. However, according to the Wall Street Journal's Business Technology Blog, a study conducted by researchers at the University of Utah suggests that even switching from a normal-sized display to a larger one—or two larger ones—has a significant effect, as well.
According to the researchers' findings, folks who use a single 24" display are 52% quicker at tasks like editing documents and tossing numbers between spreadsheets than those who use a single 18" display. Having two monitors instead of one helps, too, although not quite as much: the speed increase from switching to dual 20" displays from a single 18" monitor is only 44%. Interestingly, the researchers say productivity actually goes down when users switch to a 26" monitor, suggesting 24" could well be the sweet spot.
All in all, the researchers worked out that larger monitors can save up to 2.5 hours in eight hours of non-stop work. That said, the study assumed users had to carry out tasks that actually benefit from the extra breathing room, and it was funded by monitor maker NEC (although it was also vetted by the University of Utah's research board).