While backups are usually often considered when designing high-availability server parks, doing an actual restore is often overlooked. You simply don't want to pull a plug and rather wait for the actual disaster to happen.
Having a full file system image of a server, while space and time consuming can be the fastest way to get a server back online after a failure. If you have a SAN available, it can clone LUNs for your transparently and you can swap them back in when a machine fails or burn down. However, not everyone has one.
Using clonezilla, you can easily pull images off of Linux or even Windows servers and restore them (even using multicast!) in minutes. As it only copies used blocks, that 300 GB local disk can result in a 5 GB image. For a restore, Clonezilla restores the appropriate image based on MAC address.