The number one reason to download the entire YouTube channel is that you’re going to have offline access to them. If you want to catch up on your favorite shows but you’re going to be without internet for a while you may want to have a way to do it without the internet. Being able to get access wherever you happen to be, directly on your device, is going to be an important step. It’s going to make sure that you have something to do during that time that you’re away from internet access or not wanting to use your internet access (which is another great reason).
Many services also offer a feature called versioning. This saves incremental changes you make to files as recoverable snapshots of the file. It's useful in case you need to get back information from an earlier version or if your latest file save becomes corrupted. Services vary widely in how many versions they keep and how long they're saved. Best-in-class services, such as SOS Online Backup and SpiderOak ONE keep an unlimited number of file versions forever.