I have a 28" 4K on my desk and the picture is absolutely stunning. I'd imagine any more dense than that I'd have a hard time appreciating, but I think it matter

I have a 28" 4K on my desk and the picture is absolutely stunning. I'd imagine any more dense than that I'd have a hard time appreciating, but I think it matters way more in terms of where the display is relative to your eyes. For example, my monitor is usually about 12" away from my face, whereas my TV is about 7 feet. A 1080p picture looks just fine compared to a 4K picture at those distances, I never feel like I'm missing anything.