4K adds a lot of screen-estate. Having a "normal" 27" 4k screen, I recently worked on a ultra-wide curved screen. It blew me away. I can so much recommend curved screens over regular 4k screens. All you applications can fit next to each other on eye height.
Back in the days, many moons ago, both displays and software typically had a fixed DPI (96 for Windows) and so a larger resolution was basically the same thing as a larger display. The two were interchangeable.
In the photography and print world (and everywhere else) the resolution is just the "level of detail" or "sharpness", completely independent of the size.
With Windows 10, Windows Server 2016, and recent-ish OSX the display resolution is finally decoupled from the display size. This is especially true at nice even resolutions such as precisely double or triple the legacy 96 DPI (200% or 300% scaling).
I've been using 4K monitors for over a decade, basically since they've been available and it always cracks me up to see some people run them at "100%" scaling with miniscule text. That's not the point. The point is that at 200% scaling text looks razor sharp, but is exactly the same size as it would be at 1920x1080.. You can clearly distinguish fonts that look virtually identical at 1920x1080. It's amazing, you have to try it yourself.
Caveat: If you need (or nearly need) prescription glasses, 4K or higher resolutions may not make much of a difference for you. In this case, you're likely better off having a bigger screen and/or a very big screen further away from you.
You can select your own trade-off.
Personally I won't be happy until we have a lot more pixels to provide a larger desktop surface. And then more pixels to make fonts razor-sharp.
For my use case, at some point a very high resolution VR viewer might actually be more practical (to be able to view a very large virtual desktop)
the only caveat is that it doesn't work properly if a program is on two monitors which have a different scaling factor (i.e. the scaling from one monitor is applied for the whole program)