A clone is a bootable backup of your Mac’s hard drive that provides redundancy for both your data and the Macintosh Operating System. Cloning is easy to do and is complementary to other backup methods like Time Machine. The ability to get up and working in minutes after a crash or system update gone awry can be a very useful thing.
Clones provide a way to rollback your Mac OS X installation. You can keep your clone updated using synchronization software to perform incremental updates, and can use your clone to boot another Mac should the need arise.
