In 1999 I had 12 monitors on linux. I had coded the driver, and used XGGI (for a wall screen display).
After one week, I was down to 3 monitors, it was impossible to focus.
After 3 weeks, in professional environment I was back with one screen and virtual desktop. I tried vertical screen for code in front and an horizontal screen with web browser on the side, but a pain in the neck convinced me to keep it simple.
I since then only kept a eventually a dual screen config for fun: 1 LCD for almost everything, and 1 CRTC on a ilyama display because the black are TRUE black and CRTC makes video looks more … well, try it one day.