If the avg man knew the concept of an adblocker we would live in a different online world. I've seen people sit and watch 2 minute ads and or complain about how cramped pages are, they know they don't want ads and it's annoying but only a small percentage of that google "block youtube ads" and can click their way to install an extension etc.
That's my case - as I know that some music videos/clips will disappear soon or later for any reason (happened in the past), and as I cannot buy+download them then the only option I'm currently aware of is to download them with youtube-dl. It works reliably and it's simple to use.
In my case this often happens "in addition" to buying+downloading the song's mp3 (usually on Amazon).
I'm downloading them so I can listen without being randomly paused by youtube. Also ends up saving bandwidth massively, and mpv --no-video wastes far less cpu than firefox.