There are different reasons to Clone a copy of your Mac hard drive, but the most important one is to make a bootable backup. Why would you need a bootable backup? Even if you use something like Time Machine to backup your stuff, having a bootable backup allows you to startup onto the cloned backup drive and keep working. The bottomline is having a clone of your main Mac drive is a good idea, I have always had one. This article describes how to clone your Mac drive in Catalina using the APFS file system.