Previous threads about these filters were people complaining about them being hardcoded, completely ignoring that they are completely optional and off by default. It would go something like this:
Look at this awful thing PieFed does!
def do_the_thing():
# relatively simple code that does the thing
It completely ignored the context that the do_the_thing function is only called if the admin wants to do the thing.
Some instances have used it to do something like a dynamic message of the day. That is the most I have seen it used for so far.
Edit: See the top of the main content pane of anarchist.nexus as an example.