I keep seeing this "problem" come up, but I don't understand how it's realistic. If you have a function that modifies a parameter as a side effect, why would yo

I keep seeing this "problem" come up, but I don't understand how it's realistic. If you have a function that modifies a parameter as a side effect, why would you have a default value for the parameter? And since the site's comments seem to be taken over by link spam, is this mention on Hacker News just a clever way to juice the Google rank of said spam?