The intended use is to enable developers to very easily "Check it out" and do a Yocto Project build with minimal pain. This should allow the user to run a Yocto build and contain the required sources to do so, thereby removing network accesses as a barrier to entry. The image would be based on top of an existing desktop OS such as Fedora or Ubuntu.
With Denzil we have a Build applaince http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?h=denzil&id=d20a24310eb43fed9a3f3e75752c9ad45a18cbe4