I'm aware that this is preaching to the choir and that most of you will already have some automated yt-dlp setup running (or even stocking your Jellyfin library directly with Youtube-content via pinchflat or similar), but if you're not then I'd like to give you another reason to start sooner rather than later:
I think I'm witnessing an increasing trend of channel owners retroactively putting old videos behind a channel-member paywall.
(Maybe it's just my own subscriptions, I'd rather be crazy than right in this regard)
So in addition to content violations, intellectual-property-related takedowns, georestrictions, IP-bans and Youtube constantly doing their best to permanently break download tools I now feel I'm also racing against the channel owners themselves in trying to ensure permanent access to my preferred media selection.
If you like it, download it now. At some point in the near future it may no longer be possible at all.