While more are certainly possible and even probable, this may be a principle worth consideration - ThinkingOutLoud.DonaldNoyes.20141013
At one time when experimenting with using multiple-monitors, I had strung out five monitors across a desk, thinking this might make it possible for the display of needful information. In time, I dropped first one then another until arriving at what I currently use: two monitors.
It pairs well with how we concentrate and allocate our attention. While it is said that we can multitask up to six, it may also be said that to be effective, attention to one thing at a time is probably a good if not a best strategy to realize success.
It seems to work out this way, in using two monitors: One monitor receives attention, while the other may be used for attendent stuff which may be calling for attention, or may be related to what we are concentrating upon.
So for now at least as regards monitors: TwoIsEnough. This may be found to be true in a multitude of other situations, don't you agree? How else might this apply?
For many, one monitor is all that is needed. For others, say perhaps one who performs transactions involving many matters, three or four may be necessary, if not compulsory.
I have nine monitors on my office desk -- ten if you add the laptop I usually use. They're almost enough.
(Okay, admittedly four of them are divided -- two each -- between my Linux machine and my Windows machine, one is strictly for server monitoring, and four aren't even plugged in -- they're used to block glare from a window. That does mean five are in continuous, productive use.)
This proves that people have individual needs and styles to accompany them. As in many practices, ItDepends.
On the other end, some may have four monitors displaying one screen, to make suitable impression of WhatItIs.
+----------++----------++----------++----------+ | || || | | 1 || 2 || 3 | | || || | +----------++ ++ ++----------+ | || || | | 4 || || 5 | | || || | +----------++----------++----------++----------+I just don't have the desk real-estate for such a setup, but if I could, just think what I could show on it!
Perhaps: