Michael Michael has posted a great blog that outlines exactly how to restore the metadata through the use of powershell scripts.

http://blogs.technet.com/b/m2/archive/2010/04/16/saving-and-re-applying-the-virtual-machine-metadata-in-vmm.aspx

The saved metadata can be applied later on in the event that you add and remove the host from VMM management. A scenario where this issue comes up is when something goes wrong with your host in VMM and you need to remove it from management and re-add it to VMM (the host can also be a cluster). Typically in a situation like this you will loose all the metadata associated with your virtual machines. Such metadata includes the custom properties, descriptions, tags, owner, cost center, etc. If it is 1 or 2 VMs, its not a big deal to add them back, but when you are talking about a cluster with 200 VMs it is quite an effort.