Any site I make will have sane blue underlined links and purple underlined visited links. I’m willing to vary the shades of blue and purple, and I prefer to reduce the opacity of the underline when not interacting with the link, but I say general links should be blue and purple and underlined, and anything else is troublemaking.
(In https://github.com/w3c/csswg-drafts/issues/3012, there’s talk of changing :visited to essentially work from the site’s perspective—exposing only history that the site could have tracked itself—rather than for the user as global visitedness does. This makes me sad, though I quite understand the perspective; to me, :visited has always been about the user, even though such first-party link following is its primary use.)
I would've be opposed to a feature to disable it but I certainly wouldn't use it. I can imagine that Tor may want to enable it by default though.
Edit: Apparently Firefox has this feature and Tor does use it.
Some well-known websites do it, such as Google and Wikipedia.
I find it useful too, but since most sites don't actually show it, I'd rather just use an extension that always shows it.
Edit: oh, and Hackernews, too
I can see an option to always overridde the color with my choice.