[libvirt-users] Using virsh blockcopy -- what's it supposed to accomplish?

I am experimenting with the blockcopy command, and after figuring out how to integrate qemu-nbd, nbd-client and dumpxml/undefine/blockcopy/define/et. al. I have one remaining question: What's the point? The "replication" disk file is not, from what I can ascertain, bootable. I expect this operation to create a pristine copy of my source qcow2 file (at a given point in time) which implies that I can swap that copy in and use it just like the original. Neither using --finish nor --pivot (both appear successful) give me a mirror that seems to serve any purpose. It seems especially pointless if I use --pivot because anything that happens after the pivot ends up lost if I don't actually have a usable qcow2 file. I find lots of discussion online about getting the steps to work, but as yet find nothing about using the resulting file. What am I missing here? libvirt (1.2.2) and qemu (2.2.0) as distributed with Ubuntu Trusty. -- Gary R Hook Senior Kernel Engineer NIMBOXX, Inc