Comment Need? NO. Benefit from: Yes (Score 1) 1002
Of course they don't need one, but most of them will benefit highly from one. I generally have my code full screen on my main monitor, but my secondary monitor goes back and forth between my VCS, documentation, bug tracker, requirement sheet, and test results or trial runs of the program. Being able to have things like that open without losing sight of my code and being able to go back and forth between them effortlessly is tremendously helpful
More rarely, it has older code on it as I copy and past from one project to another. Then being able to see the two projects side by side is of great benefit.
So, I get a lot of productivity benefit from the second monitor, and I think 3 would be quite resonable.