This is good advice for most people in general. Speaking slower gives more time to think about what you're going to say, which means you say better things. It's shocking how slowly you can get away with speaking.
Incidentally, slowing down is also good advice for improving your handwriting.
Importantly, for topics that I don't understand (learning a new language - Dutch), I often don't speed up those videos because my brain is working a helluva lot harder to keep up. This changed last week however, when I was watching some very basic A1 content and found myself wanting to speed it up just a little bit. Did it help that the presenter was speaking slow and enunciating? Yes, but it's nowhere near the most important deciding factor (imo).
You'd probably miss out on quite a lot more if you played a Platonic dialogue back at 2x speed.
javascript: (() => { document.getElementsByTagName('video')[0].playbackRate = prompt("Set video speed multiplier:", "3"); })();