Why datahoard?
Contrary to popular belief, stuff is deleted from the Internet all the time. Sometimes it's because of censorship from outside of the sharer's control, other times it's self-imposed censorship thanks to pressure from the cancel culture we now live in. On top of that, there's link rot and just general loss of information. Only 44% of all videos uploaded to YouTube in 2010 are still able to be watched. Videos and channels are still being lost today. If you hoard them before they go down, they won't be lost.
Another reason is that hoarded data requires no internet connection to use assuming you store locally. Want to watch a new video from a channel you like, but the internet is down or too slow to stream? Not a problem if it was downloaded beforehand.
This extends far beyond my example of YouTube here. There have been many times I came across dead links or found that something I either wanted or had downloaded in the past that had been wiped from the internet.
How can I get started?
Check the first few links below. My advice would be to buy high-capacity external drives during holidays (especially Black Friday), and if needed simply remove the drive from the plastic case for use as an internal drive.
By the way, you should ALWAYS have a backup. When you buy storage, assume at least half is going to be part of your backup. Remember to test your backups as well, or else you have a Schrödinger's backup that may not work when you need it.
Having good backups is especially important for irreplaceable data. The 3-2-1 rule is a very good one to follow here; three copies of your data, two on different kinds of media, one being stored off site. If you can just download something again, having multiple backups isn't as important (although having one can save you headaches).
Legal note: Piracy is bad because copyright and intellectual property and I am not in ANY WAY being coerced into saying this there is NO ONE threatening me my FAMILY is SAFE and I don't want ANY OF YOU illegally downloading anything DO NOT.