In a couple of decades running Linux installations of all flavours, I have never seen anything in lost+found!

Yea, run an old kernel with ext2 on a busy system writing a bunch of small files and have a power supply fail and you'll end up with something there.

fsck on large hard drives was scary on how long it could take to finish.

You need to use worse hardware and bad power :)

Same here. And I had some pretty f**ed up file systems.

At one point, I had one where the directory structure was completely broken and had circles in it (broken SSD). To be fair, in that particular case, I did not look for lost+found and just wrote a tool to extract the data manually that I was looking for.

That's what the answers are missing, of course. In some filesystem formats, it's possible either to recover completely from a journal/intent log, or at least to recover everything to the point that recovered files can be placed into the correct directory.

Have to run fsck. This used to be forced about once a month but don’t remember it happening in the last decade or so.

My SD cards have always had stuff in that folder. It scares me. I try not to look