Ooh, this topic has piqued my interest
It's definitely handy to download and save videos from YouTube (or really, anywhere for that matter). I've actually been recently picking up more steam on downloading and saving videos (though I have been doing this for a while) in case YouTube either age restricts or removes a video straight up, or if a video is privated by the channel. I've done this for YouTube Poops, nostalgic videos, random videos, even some series like Terrible Mouse & Helluva Boss. Then again, I only really save videos in 480p since I personally don't need the typical "4k" or "8k" resolution since I'm not gonna be seeing these on a huge screen.
One thing I use to download videos is
NewPipe, it's a frontend for YouTube for Android devices that I
LOVE using to not just watch and listen to videos but to also download (and even watch and listen to stuff from other platforms like SoundCloud for instance!)!
I personally use a fork of NewPipe called
PipePipe, which not only broadens the kinds of platforms I can watch to NicoNico & BiliBili but also implements Sponsorblock, super handy to skip all the ramblings and get straight to the meat and potatoes of a video.
NewPipe and its forks can download videos in a broad range of video and audio qualities. The default for me is AVC1 480p for videos. I like having MP4s
Another tool I use is
cobalt.tools, which has come in handy for saving stuff that's not just on YouTube but elsewhere as well. Broad range of supported platforms though it has been trying to work around the issue that YouTube has these days.
There's also
Invidious (it's more of watching videos but I feel it's good to mention here), which is a YouTube frontend for browsers. I swear there used to be plenty of instances but now there's a few thanks to
again, YouTube being YouTube.Saving and downloading videos feels good, man.

If you know of a video (or really any media) you really like, it's good to save it before that platform has it next on the chopping block.
Good to have backups of what you save too, in case one spot isn't working.