I have recently switched from a Apple thunderbolt display to an 27" 4k display from Samsung. I can't speak for other platforms but OSX lets you use the 4k in "r

I have recently switched from a Apple thunderbolt display to an 27" 4k display from Samsung. I can't speak for other platforms but OSX lets you use the 4k in "retina" mode thus doubling the pixel density. So you end up with incredibly sharp text. Since it is possible to adjust the scale via software you can adjust for more space / better readability depending on the needs at hand. For me the switch was as big of a switch as going from low-res to hi dpi phones. I really love that you can have good legibility with much smaller text in editors / terminal. After all I can say that while I am missing the docking / hub / power plug / webcam features of the thunderbolt display (colors where also better) due to the increased sharpness and the (perceived) productivity gains I would never switch back to less than 4k for a workstation screen. So purely subjectively speaking: 4k is just the business.