This seems silly but, everyone once in a while something goes wrong with a deployment customization spec. So, if you every run into a situation where you have deployed a bunch of VMs, only to find out the spec is broken. Simply poweron all the VMs, let them run throught the peding spec. (I have not figured out a way around that part). Then power them all off,
shutdown-vmguest
shutdown-vmguest. Remeber to remove them from AD if they joined already.
Run
Set-VM -OSCustomizationSpec "yournewspec here" -Confirm:$false
Pretty handy if you are deploying large numbers in the hundreds. You don't want to have to redeploy 300 machines. Of course, you could get it right the first time.

Hard fast rule, even if you tested within a week, make sure you test the inital vm before deploying big numbers.