Cloning a Mac hard drive creates a bootable backup that allows you to replace the primary drive or troubleshoot operating system issues. It copies all files, applications, and user data to the new drive, maintaining the same functionality. Cloning provides an alternative booting option, allows testing applications and identifying issues on the clone without affecting the main system, and ensures work can continue if the primary drive fails by booting from the clone. Stellar Drive Clone software makes it possible to clone to an external solid state drive for faster performance than a standard external hard drive.