We transfer our backups to S3, so there's always a chance that it could be corrupted during transfer, or that the compression could have failed before transfer.
It can also help catch operational changes, eg. someone changed the root password and updated the apps that depend upon it, but didn't adjust the backup scripts.
It can also help catch operational changes, eg. someone changed the root password and updated the apps that depend upon it, but didn't adjust the backup scripts.