Cloning Disks
The disk cloning tool will delete all files on the destination volume if you clone to this disk for the first time. Deleting files can take some time. To save your time, you can erase the destination volume using the Disk Utility application beforehand. There is no need to erase the destination disk when you clone to it the same source disk again because most of files can be reused.
Notice that on macOS 10.15 and later, there are two commands for cloning in the main menu. The Start Clean Cloning command should be used for the first time (e.g., when you clone to an empty destination). This command formats the destination volume and replicates your disk volume with help of the asr (Apple Software Restore) utility.
The second command Start Cloning is used to update a previously created clone. On systems earlier than macOS 10.15, this command is used for both the initial and repeated cloning.