Before I got my 4K display I tried using a 24" 1920x1080 monitor in vertical orientation, and found that even though 1080 pixels wide should be enough to render any website fine, some websites (including some pretty big/important websites) started treating my screen as a mobile device screen, hiding many elements and giving me the mobile view/UI. I guess those sites weren't detecting user agent and were detecting screen resolution? Idk but it was annoying.
Got a 27" 4K screen last year and I have just left it in landscape mode...it's been fine.