It's a bit puzzling to me, how many YouTube mirroring tools are available out there. If you're using something like that, what's your reason to download/archive the videos instead of just streaming them from YouTube? I get that sometimes it's great to archive a video in the case it get's deleted from YouTube, but in my case this very rarely happens. I watch the video and I'm done with it. If I can't re-watch it, this…
For me, the same reason people used VCRs, and I don't mean "copyright infringement" --- saving stuff to watch later or when I don't have an Internet connection, or only a slow one. The majority of what I download only gets watched once and deleted.