Sometimes things are so obvious to me I don't even think they'd be worthy of a discussion. But this is one of my blind spots, as I've come to realize over many years.

For development, I've always been happy with a 13" screen and nothing else. Not only that, but having all apps in full screen. It brings so much clarity to my mind. Exceptions (because f*ck dogma, right?) have been when I was in charge of monitoring some long-running process, in which case a secondary screen in vertical layout was very useful. Another one was for music making with Ableton Live: 2 screens was much more practical, independently of each individual screen size.

Just because of the setups I've just described, I've been looked at weird, or asked way too much questions. go figure.