Backing up the data is not sufficient - you have to restore it, too
When was the last time you restored from your backups?
If you answer "never" (or even anything approaching "quite some time ago"), your backups might well be completely useless, for all you know.
Without testing the restore procedure once in a while, your backup process is a waste of time. Literally - you're replacing one random risk (the chance that something will destroy your data) with another (the chance that something will destroy your data, and you've been backing up only the zeroes(*)) that's only slightly better.
When you need to restore from a backup, that's the worst time to find out that you can't restore from a backup.
(*) Now, watch, as someone links to this article and tells the world that I'm advocating cutting your backup time and space in half by only backing up the ones. What I'm really advocating is that you backup your zeroes to one tape, and your ones to another.