The text is sharper with a higher PPI even if the actual size of the text is the same. I have a 4k 24" screen, and text is much much sharper than on any FHD 24". Hell, it's noticeably sharper even than on my 14" FHD laptop. And sharper text helps with legibility, so I find I can actually use smaller font sizes more comfortably than the "regular" size on a lower-res screen.
You don't get more real estate, indeed, since that depends on zoom level. However, depending on your setup and habits, you may actually gain some. In my case, I use 4k at 100% zoom. I don't care for window decorations, interface icons and so on, so it's not an issue if they're small.
You don't get more real estate, indeed, since that depends on zoom level. However, depending on your setup and habits, you may actually gain some. In my case, I use 4k at 100% zoom. I don't care for window decorations, interface icons and so on, so it's not an issue if they're small.