I used to have three 1080p screens. Now I just have one 4K screen, and I still have more screen space :)
I personally like to use Divvy to chop my screen into sections but mostly I do 2/3 for my IDE (affords me 3 less-than-full-width columns for source) and 1/3 for the browser. I have wanted to have an iPad for displaying docs but haven’t gone there yet.
I love it and it's just a $200 TCL TV that happens to have good response (thanks rtings.com).
Both the portrait displays get a good amount of use. The central one is most important of course but the one to the side is useful too as I don't have to turn my head much to look at it. Its usual use is documentation or similar but using it for actual work is no hardship.
The landscape display is mainly there because I work in video games, so I kind of need one. I usually use only about half of it at most, though, to avoid having to turn my head too much. If I was in some other line of work I'd probably have a 3rd portrait display instead.
(I did use the large monitor + laptop below arrangement for a while, and that was good too, but one day I knocked my drink over and it destroyed my laptop. So that prompted a rethink.)
Every now and again I use them as a reference screen against something I'm doing, but my neck starts hurting pretty quick. Alt-tabbing rocks. They tend to be mostly empty.
Alt-tabbing means improved focus "one thing at a time" too.
I'm thinking to keep a large 32" screen in front of me, ditch the side 32" and get a "portable LCD" to put "under" as if my keyboard is a laptop and I'd have a laptop screen below my main screen. That should be hopefully useful as a reference screen.
Having 2 or 3 of the exact same screen makes no sense to me anymore. We're not with 19" CRT Sony trinitron anymore :)
I'm surrounded by a wall of screens and I don't know what to do with them (that is useful and not distracting).