[soneca]

I can divide my screen among several windows to perform one task.

The most obvious example for me is coding. Terminal, code editor, browser running the code locally.

Even when I want to have a break and check HN I prefer to open another tab on the non-fullscreen browser for an easy transition to and from the break.

[bryanrasmussen]

most people I see do this do it on multiple screens not multiple windows on one screen (or multiple tablet sized windows on one large screen, and most do it without making any screen as extremely narrow as the parent did.

However I suppose also that most is not all, and there must be some outliers who do it on a single laptop screen either from necessity or preference. I might find myself doing extremely narrow windows out of necessity but never preference, and then the extremely narrow windows would almost always be on something I was working on - as it is indeed in your case - and not to interact with someone else's site.