I would run Windows Vista if it was the only OS with multi monitor support. Its absolutely crucial for my productivity.

absolutely. I find a pretty common workflow for me is writing code in one window while having documentation (or a header file) open in another. it's not the end of the world if I have to alt-tab back and forth, but it's much more efficient if I don't have to.

a 24-27" monitor suitable for coding is only $200-300. if you code for money, it seems like a no brainer to just get two.

Crucial.

I've got an entire monitor (really a 55" 4k TV) devoted to all the chat windows and communications I'm running for my team, another 4k monitor that I actually use to code, and then my laptop sits to the side as an auxiliary monitor where I can look things up and what not.

Yes, they are that much of a benefit.

Until this pandemic forced me to make do with one monitor at home, I rarely used the built in screen on my work laptops; I counted on the dual monitors on my desk. The idea of using a laptop display alone is baffling to me.

It is an improvement, but not as much as some people claim. The issue is you need to move your eyes/head too much.

If you have a wide or ultra wide monitor, it is better. Otherwise, a good desktop manager with virtual desktops helps a ton.

I've tried multiple monitors a number of times through the years, and it's only been a net benefit when doing things like streaming and/or presenting via video conference (so you can have a preview monitor / live chat separate).

Other than that, my brain and neck both work a lot better with one large 4K display (currently 27" but I've been thinking about going 32").

I made this switch. After a couple years of a single (but larger) display, I can enthusiastically say I like it much better. I have the Dell UP3216Q.

and this is why I still use two 20-inch 4:3-ratio monitors in portrait mode (combined screen is 2400x1600) -- I can look at each monitor with minimal neck movement and the viewing angle for each half is independent. when i've tried a single, curved ultra-wide I still felt like the outer third on each side was a tilted away too much

I have one horizontal monitor and one vertical one. Code lives on the vertical, everything else on the horizontal.