I’d never really thought about it, but this from Mat Duggan is absolutely true for me:
[O]ne big monitor is a a different experience entirely compared to 2 smaller monitors. I don’t use the two monitors as one large unbroken screen, I tend to use one of them for “less important static content” like a ToDo list or my work chat tool and my email and then the “primary” monitor for my terminal/tmux/browser which is how I do all my actual work. But windows “belong” to one or they “belong” to another. Grudin found in 2001 that people use a second monitor exactly this way, where focal work on one, peripheral glances on the other. Twenty-five years ago. The OS still doesn’t know which monitor is doing one role and which the other.
The whole thing is about his ideal UI, and I haven’t done more than skim it, but it definitely seems interesting.