There are several reasons I do this, and most of it comes down to not trusting Youtube to keep content available consistently for the various reasons others hav

There are several reasons I do this, and most of it comes down to not trusting Youtube to keep content available consistently for the various reasons others have listed. There is an added benefit. I have one channel I follow that does a LOT of q&a type videos from the audience. Because I download the subtitles as well, I can throw those into a database with the video titles and make a searchable database if I want to see what the host has said about a particular topic. I don't have to rely on my memory or go hunting. I can just query my database and know exactly which video/timestamp has the topic I'm looking for.