The increased sharpness/crispness of a 4K screen considerably improves the usability of the screen for me at a 1080 setting.
I usually sit quite a way from the screen (≈1.2 metres, about 4 feet), which means the system text on a 1080 setting is a good size for me. Plus I am in my 60s with some vision issues so text on a 27" running at native 4K is just not workable at any practical viewing distance, let alone 1.2m.
1152, 1296, & 1440 res are all reasonably sharp for me on the 4K 27", still better than the old native 2K 27". But 1152 only gives a marginal gain in usable screen estate, and system text on 1296 & 1440 is still too small.
I am planning to move to a 4K 32" for my next monitor, partly for a bigger movie screen, and partly to see if I can use it at native 4K res or 1296/1440 scaling.
Also might switch from the monitor mount from a stand to an arm, to help fine tune the set-up.