You can do that of course, but I think the important issue is how you keep such back-ups current in real time. A back-up is only a useful snapshot at one point of time, so it needs to be an on-going process that isn't cumbersome to maintain. I used to count on Time Machine for this, but stopped doing that after a drive crash and I realized TM back-ups are not bootable - my bad, should have read more carefully.
Power up your Mac while holding down the Command and R keys to enter the OS X Recovery Partition. ...
Select Restore from Time Machine Backup and click Continue.