yes, because google has a habit of removing content from youtube, even educational content. (they made a policy to remove infosec content last year which they deem dangerous)

moreover, some youtubers remove their stuff

Youtubes copyright enforcement can hit videos at random, parodies like DBZA have been lucky enough to reappear after a few months. Other channels discussing movies or really anything else that might contain a few seconds of copyrighted music in the background can suffer random bouts of silence. So there are good reasons someone might feel the need to keep a personal backup outside of youtube.