This strikes me as being really useful, especially for clouds or large server farms. There's a lot of value in having a server be in a known state.
It also seems to me that it fits in to some other changes that seem to be taking place. We used to think of computers as things, physical objects. But to a certain extent, "a computer" is becoming a blob of data that exists in some sort of container (ie., hardware).
My main desktop, for example, is a blob of data that lives at a VPS hosting company. Some people carry around their systems on USB sticks, and boot them wherever they happen to be. Etc.
If a computer is a blob of data, then having better tools with which we can describe and build these blobs is a really good thing.