The 'offline' one I agree with, but don't think that's precluded (they have the chef recipes, so why not); but it's an option not the common case. And the last one too - we've got a similar setup, and there are times when there were issues with our xen vms that we explored outside of the shared cluster. One more justification would be overflow - this has happened here, we don't have room for all the VMs on the cluster so some of us run them locally.

So yes, don't rule it out, but still seems to make economic sense to share hardware.