I use Acronis to back up to an external WD 3tb drive.
If I ever find myself in a position where my c drive won't boot at all, I stick an acronis recovery cd in my cd/dvd drive, boot to it, select the backup file that I want to restore, restore it and I'm back to where I was when I backed up to that backup file.
I setup up a rotation of three backups of my c drive, two each of my d and two each of my sample drive so all my drives are constantly backed up.
I typically back up my c drive daily, and my d and sample drive when I deem it necessary because of changes to the contents to those drives.
I have had to restore my c drive on occasions in the past and the restore worked fast and flawlessly.
I also have acronis set to verify the backup image when it backs up just for piece of mind.
Remember, you can only do a restore to the last time you backed up so if you backup up only once a month, let's say on the first and you suffer a bad crash on the 31st, you can only restore the last backup you ran on the first and you lost a month's work...