As peculiar as it sounds, I had no idea if I'd see a clear visible difference from moving up to my new 4K HiDPI display before I got it. In fact I more or less expected it to not be a big change from my previous monitor (a 24" 16:10 Dell U2412M). I'd read people raving about the Retina displays on Mac laptops, but people have different standards for what they consider rave-worthy (and what they notice about displays). And it wasn't as if my existing display was clearly pixelated or low-resolution, the way old computer displays definitely were. I though that perhaps I already was in the zone of diminishing returns for increased display density.

A little bit to my surprise, it turns out that my new display does make a clearly visible difference. I didn't see this right away, when I first set it up, and even after I'd used it for an evening or two. What it took to make this really apparent was having my environment settle down and then going back and forth between work (where I'm using Dell U2412Ms) and home. I use the same fonts at almost the same physical size at home and work, and after things settled down it was clear that my home display was visibly crisper and clearer.

Interestingly, the really clear example for me was the / character in terminal windows (and thus in a monospaced font). At work on a 94 PPI screen, I could notice that it had a bit of 'staircase' pixelization; not glaring or obtrusive, but the kind of thing I could see if I was paying attention. At home, on a 163 PPI screen, there are no pixels even if I peer closely (far more closely than I normally am at); it's a smooth slanted line.

(Now that I've noticed this effect at work, I can't unsee it, which is a tiny bit annoying. Fortunately the monospaced / is the only character where I'm really conscious of the difference, although other characters are also better and crisper.)

Text isn't the only thing that looks better at the display's resolution, either. Many program icons are sharper and nicer to look at (although some of them may also be physically bigger, because of scaling issues). Pictures in things like web browsers are a somewhat more mixed bag, but a fair amount of the time it works well (sometimes they get a bit fuzzy, presumably because browser scaling can only do so much).

Following my standard views, I haven't attempted to use physically smaller fonts on the new display. Small(er) fonts might now be more readable than before because they're crisper and smoother, but I still feel no particular urge to find out or to squeeze more text into the available space.

PS: My new display may also be somewhat brighter, which may have its own effects on apparent crispness and readability. I haven't gotten around to even checking the brightness and contrast settings at work, much less planning out an experiment to give me some sort of light level value (although smartphone cameras and the right apps probably make it possible).

Sidebar: Why I bought a 4K HiDPI display despite uncertainties

I've been looking forward to high-DPI displays for some time for their advantages in crisp, high resolution display of text and other things. I've been around computers long enough that I've seen screen text go from being clearly low-resolution pixelated fonts to being much better, so I was all in favour of taking another step forward toward screens that would look as good as print does. That was my logic for persuading myself to get a high-DPI 4K display; I'd theoretically been looking forward to it for years and ones I considered reasonably affordable were finally available, so it was time to step up to the plate.

(I'm very good at sitting on my hands and not buying things, even things I'll enjoy. It's not logical, but people aren't logical.)