> So if you want to use for example maps on one tab and read text on another, the best UX would be to have users resize their browser when changing tabs?
The best UX would probably for text and maps in this example to be in different windows, to be honest. But that causes other issues with the mental model people have about web sites. Still, having a website-provided width limit helps avoid a click or two required to split the site off and resize its window, at the cost of wasting huge amount of screen space.
Not sure what's the way towards a better UX, though. I myself like tiling window managers, in which I can efficiently position stuff with keyboard the way I like, but I understand this will be too complex for casual users. I also like grid window positioning, like http://windowgrid.net/ which I use on Windows, which lets me flexibly resize windows with the mouse while retaining a nice looking layout. I feel that a solution like this would be simple enough for regulars, too, offering them useful flexibility with little confusion.
But I agree that I commonly see people having their browser window maximized all the time (on huge monitors, to a great waste of on-screen space). I think the fact that they became accustomed to that is an unfortunate consequence of modern web design.
Of course, the Windows users whined and whined and whined about that until Apple decided to make everything go fullscreen super easily.
So anyway, I love seeing people use 34" ultrawides to browser websites with their browser window maximized. It's a ridiculous waste of space. XD
now whether these people are aware of that and whether they say that having 2800x1200 window is fine for them is a completely different thing...
There are few reasons why a line of text should be longer than, say, 800 (css) pixels, but having the browser full screen might still be a good idea for more app-y sites.