I mean, in some sense your two cases are indistinguishable since there's no way I'm going to inject ads into my local .mp4
However, I'd guess quite a few folks use yt-dlp for archiving (or watching on an airplane) because YT Premium is not a "we promise this video will still be available next month"
Yep, downloading copies of videos so I can watch them on long flights is one of my main use cases for yt-dlp.
I suppose someone more sycophantic to the wishes of trillion-dollar corporations could argue that I'm not entitled to do this for free, and that YouTube offers an offline download option as part of its $13.99/mo Premium offering. To them, I'd say "you're right, also go pound sand lol."
However, I'd guess quite a few folks use yt-dlp for archiving (or watching on an airplane) because YT Premium is not a "we promise this video will still be available next month"