Confession time: if I'm doing something quick and disposable in raw HTML I still just throw in a <center> tag, because I can't be bothered to screw with CSS centering when I need something to just work, and right now.
[EDIT] I'm talking about situations like "we need an ugly informational page here for an hour" and all or some part of it would look better centered, or if I'm throwing up a placeholder page on a personal site. Those kinds of things, I'm not gonna google "what's the correct 2020 CSS to do what <center> does" and end up with a bunch of caveats and gotchas when I could just <center> and move on with my life.