If you have a Mac you probably use Time Machine, which is great to recover a lost file or so. But what if your storage drive (HDD or SSD) failed, which is rare, but can happen. Could you then recover everything you've lost? You could if you've done a clone of your drive to an external drive.
This is a simple process, and external drives are quite reasonable in cost nowadays. There are many programs available to clone your Mac, and here is an article comparing the different options. I've used Super Duper for years, and thankfully have never had to test it. If, say, the drive in my Mac should fail, I would replace it (an SSD), then plug my external drive in and reload everything I had previously on the drive -- OS and everything! I'm up and running again.
You hear the terms clone and image when referring to backups. What's the difference, you might ask? Well, you probably don't even care, but if curiosity prevails, read on. Here is an article that describes the difference in the two processes.
The important thing in all this is to have a bootable clone of your hard drive. If catastrophy should strike, you can quickly recover.