YT videos get taken down for any reason these days - fake copyright claims, hacking or just the creator getting fed up with YT’s policies. Entire channels vanish with no warning. Valuable videos that generate income suddenly become private only. It is not an open platform, it’s a monetised platform first and foremost.

If you have these videos under your control, then if they’re no longer watchable online, you still have them. That’s exactly what TA is for and does a superb job of. Basically every YT video I watch that I think is useful, I hit the Save button. Some of them are indeed no longer available. I have entire channels downloading so if the creator does close up shop, at least I’ve got their latest.

Obviously you need a lot of storage space - mine is over 5TB and growing. But it’s worth it.

Also, it avoids the YT before, mid and after ads.