[Piskvorrr]

You can then e.g. run a static analyzer over it, which can say things like 'in SomeOtherFile.php:130, you're passing $config="nope"; this is a string, not what the function expects to handle' or 'html2wikitext is supposed to return string, you're returning a DateTimeImmutable at line 160'. Same with the access modifiers: 'private function whatever() is unused'.

Further, documentation: "of course everybody knows what you're supposed and forbidden to pass into $data" - NOT. Even if it's just you writing the code: the you+1year will have trouble reading it (been there). Not even when it's supposed to be documented. If you have an explicit data structure, this becomes far more evident, even before any documentation (note: not replacing it).

I'm not interested in playing computer in my head any more, juggling internal state that's completely superfluous to me: am I a higher primate? Yes. Are higher primates tool users? Also yes. Should I let machines do the menial tasks for me, leaving me to do the creative ones? A hundred times yes.

(NB: this is not a silver bullet - e.g. won't help against logic errors - but it's a useful guard against going completely off the rails)