Sometimes two smaller displays provide a cleaner division between work tasks.
I found it difficult to manage my 30" display while working simultaneously in ArchiCAD, Photoshop, Adobe Bridge, Word and InDesign. Things slid around a lot. The book layout was 22" wide, so at least the full spread would fit at full size.
Occasionally you just need a place to put something off to the side.... so no matter what huge display you might have, a tiny tick bird display is helpful.
As for smaller is better: if you have any strain whatsoever while testing, things won''t get better, especially as you age. The smaller displays can deliver the pixels, but to the point of being impractially small, especially dialog boxes.
Dwight Atkinson