The most damaging thing that can happen to an organisation's computers is a total loss of data. After a catastrophe you can replace computers fairly easily but companies often find it difficult (or even iompossible) to recover from a complete data loss.
The most common causes of total loss are theft of the computers, fire and flood. In each case, the only route to recovery is through a set of backup files which are always held off the premises either in the form of backup tapes, a memory stick, or DVD disks - or via an internet backup facility where files are synchronised every night with a backup copy at an off-site location.