Most traders wouldn't need so many screens... But if you are a day trader running multiple trading platforms and software etc - then it is much more efficient to have everything on disply at all times...
Otherwise opening and closing windows all the time on a lesser setup to access information is time consuming and reduces focus when considering how many times you wou have to do that as a day trader throughout the day...
It's a pretty low investment to have such screen space compaired to the increased productivity you gain...
