Current use of webfinger, host-meta etc mapped to public.php?

It appears that the .well-known entries mapped via redirect to public.php (per this section in the docs) respond with 404s, unless a PHP file is registered as a handler with something like:

occ config:app:set --value foo.php core public_webfinger

At least that’s what I can gather.

Now: how is this functionality currently used? There are some posts on this forum that indicate the social app uses this (perhaps with some glitches). How exactly does it do that? Automatically set that value upon activation? Something the user is supposed to do?

Are there are apps, or other scenarios, in which those or other handlers are being registered / used through public.php?