Since you ask, I'm using a 27" iMac of the final generation before Apple stopped doing 5K iMacs. And yes, there's a teeny-tiny difference in clarity if you lean into the screen and stick your nose 1cm away from it. But at any normal reading distance that isn't designed to destroy your eyesight, the difference on such a retina display is basically not visible. However, the smaller file size makes the file appreciably quicker and smoother to render (even on a fast modern machine) as well as being more economical on disk space. And yes, that's a minor issue on a multi-terabyte computer, but why not be efficient if you can be? I always try to optimise the PDFs I create myself as much as possible, because wasted storage soon adds up, and smaller PDFs just perform better anyway. So I stand by what I said.