I used to be completely dismissive about these videos but then I began noticing that you can hear some differences provided the poster has set it up correctly. Obviously no critical listening can happen over YouTube, but, as others have said, you can get a taste of what a particular speaker sounds like and can certainly pick a favorite among two or more that are properly compared. I’m much more cynical towards other equipment, cables, etc. than I am speakers, but who knows, maybe I’ll come around on those someday, too.
I should add that I have a pair of fairly good Audioengine powered speakers connected to my iMac, with very good headphones available if I'm really interested.