One of the most basic emergencies is the loss of data. In a worst case scenario the building that houses the system burns down, and all the data is destroyed. Having a hard drive go bad can also result in a complete loss of data. Partial loss of data can be caused by a number of things from a virus to an accident with rm . In each of these cases the system can be rebuilt, but without a backup it cannot be restored to its original condition.
Backups can also be valuable security tools.