Disk storage is local, as everyone else here has said and cloud storage is storing files over the internet on a server that is located somewhere in the world. Now. There's a problem. People rely on cloud storage. The cloud will never go down, as they claim.
So let's see, a tornado hits right where the servers are that are storing YOUR data. You've run into a computer issue, and you need to retrieve those backed up files from the cloud storage. OH wait, your files, they aren't available, the servers are down!!.
Use disk storage. Disk storage CAN also mean, storing files onto a DVD disk or a CD disk, and not just on a hard drive. But you know what, I trust my physical media more than I would trust any cloud storage, because I have that DVD disk or CD disk in a jewel case, right at my fingertips. If I would need to reformat my PC, I have every file that I would need, without any internet.
I have DVD's mostly, that are 10+ years old, that work like they were created on day 1. There's absolutely nothing wrong with using disk storage. Yes, hard drives can fail, but generally speaking, they won't fail unless they are being thrown around or something like that. And unless a drive is like 15 or 20 years old, it could certainly slow down and begin to show its life.
Again, people rely way too much on cloud storage, and I, I would never, ever trust my files with any sort of cloud storage. Yes, while the cloud is up it's convenient, and yes you wouldn't really have the need for disk storage. But, there is always, ALWAYS, that one, small chance, that the cloud goes down, and you have no files.
Just something to think about if you wanted to use cloud storage over disk storage.