Without my glasses, sure. But to give a personal example of what I mean by the ability to “see”–I used to not be able to recognize what wigs look like, at all. After I started to cosplay and acquired both personal experience and learned from skilled friends, I now can’t unsee certain wig tells. If people don’t know (how) to look for a thing, they literally might not be able to see it–thus, whether changing settings gives a noticeable difference is a bit subjective.
So, from my testing (with SSAO on Low, given the topic) here’s all settings at 3.8:
And all settings at 4:
The only differences I am personally seeing, via both screenshot comparison and live switching, is that having View Distance set to 3.8 turns off the very far way, stronger middle glow effect under portals (leaving the spinning glow on). World Detail also made a distant teleport pad disappear. (It suits to reason, if there was grass, turning down Vegetation Detail would remove some of it at the same distance.) However, neither made the test dummy disappear, and the very very far away spinning glows were on with both settings, so only a few small things are lost.
None of the changes I see here are things that I would consider “a noticeable decrease in quality,” given that I had to flip between two screenshots several times to even notice them. Starsmith’s example of losing water reflections is the biggest change I’ve seen, and that one only applies in areas that have water.
Of note, actively changing the GFX settings does mess with a whole bunch of things–it turns off (at least) AA and depth of field (the latter stays off until relog), whether you’re turning it up or down. When you turn GFX down, it auto-sets SSAO to Low, and when you turn it back up, it auto-sets SSAO to High. It should go back to whatever you last had in the dropdown on relog…but those passive changes mean you have to adjust a few things manually to get a proper comparison without a relog.
Now, if anyone figures out how to turn off bloom without having to strangle GFX… 