This is how I use the browser - 1920px is way too wide for reading, and I like my browser windows in portrait mode for more vertical space anyway. Unfortunately, yet another idiotic "feature" of javascript (and CSS media queries) allow the webpage access to the actual monitor resolution. Some particularly idiotic sites use this, causing utterly unreadable pages (i.e. all "sidebar" and margin) if you have your your window at something like 900px wide instead of the 1920px they are detecting.

This is mostly the websites fault, of course. It's the same forced-layout mentality that has always caused problems on the web.