4k users often use font scaling which makes things harder to compare to a standard full HD setup (different people use different font scaling options etc). When

4k users often use font scaling which makes things harder to compare to a standard full HD setup (different people use different font scaling options etc). When developers setup makes dogfooding more accurate (in terms of similarity to end hsers'), then more UI bugs are found sooner. Another thing is contrast and hue - many users use low quality screens (think office users) and they perceive the UI differently than a person on a high end monitor. Many subtleties are not visible at all.