Migrating to Lync 2013 from OCS 2007 R2 ... to unprep or not to unprep

Question

I've been reading on TechNet that I should unprep the domain and forest after decommissioning / uninstalling all OCS 2007 R2 server roles:
http://technet.microsoft.com/en-us/library/dd572243(v=office.13).aspx
...but then, in other places (such as blogs and TechNet forums), I've read not to unprep the domain and forest if Lync 2013 is already deployed:
http://social.technet.microsoft.com/Forums/lync/en-US/6b8cd7ca-fe67-418b-ae66-5be682d8d2d6/unprep-ocs-2007-r2-domain-and-forest-with-existing-lync-installation?forum=ocsplanningdeployment
http://www.ucprofessional.com/2011/04/decommisioning-ocs-2007-r2-after.html
Would someone please clarify what to do here and why?

Answer 1

While I haven't personally done a deep dive on everything it does, my understanding is that's it's more than just a simple mod to the system container.  For example, from the OCS decommission article you referenced: "Running
Unprep for a domain removes the access control entries (ACEs) granted to Active Directory universal groups".   Lync still uses the same RTCUniversal groups, so touching it at all with Lync in production as well could be bad. 
Forest prep actually creates these groups: 
http://technet.microsoft.com/en-us/library/dd441353(v=office.13).aspx  That said, I haven't seen an unprep referenced in the migration from OCS to Lync docs, and the doc you referenced is specifically for completely removing OCS from your environment
where these groups wouldn't be needed.  So, while I can't tell you exactly what all it does, I really wouldn't mess with it unless you have a strong reason to or are willing to rebuild Lync to get a few old objects out of the system container.
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