Disk cloning or Clone a Disk is the process of copying data from a hard disk to another one, in fact you can do this process by copy & paste but you won’t be able to copy the hidden files and folders or the in-use files, that’s why you need a cloning software to do the job, also you may need the cloning process to save a backup image from your files and folders.

Source: How to Backup or Clone a Disk in Linux by using Clonezilla | Unixmen