Devs how much does an extra screen help in programming like reading documentation while coding etc

Always use a second screen. One with the IDE open and the other one with documentation or just some console or debug window open.

A second screen is also quite useful during online meetings or chats on one screen while viewing stuff on the other. If you share your screen during a meeting, you could just share one of the screens and have something else open on the other one.

As a web developer, my primary use for a secondary screen is to display some sort of preview for the site I am working on. If I'm doing any kind of frontend development, having an immediately visible live-preview can save a lot of time.

Outside of web development, secondary monitors are nice to have for documentation, watching tutorials, managing multiple code editors, and more.

I still find myself coding on my laptop around my home often enough that I wouldn't say a secondary monitor is necessary, but it's certainly helpful.

I have one screen at home, two at work. The second screen is surely nice, but I wouldn't call it mandatory. To put it other way round, the lack of a second screen at home is occasionally mildly annoying.

Making use of virtual desktops and auto-tiling gets you 80% towards a second (real) screen.

Also: Having a second screen makes you wanting a third one earlier or later.

While coding I use the extra monitor for -

1. Docs, stack-overflow or googling
2. Checking the output while doing web development.
3. Playing anime as noise XD weird but helps me to concentrate.
4. Browser console to check the logs, on primary monitor I just toggle between browser and code editor.

While designing you obviously need some space or you'll end up scrolling and changing windows a lot; and multiple monitors are still cheaper than ultra huge monitor.

PS: Moving your eyes from one monitor to another takes some time, there isn't a lot you can understand from your peripheral vision. So instead of switching your eyes, you just end up looking at one monitor for ~80%

As someone who just packed me second screen away. Honestly not a huge deal. But it's an ego boost I guess. Is the ego worth the money?