Let me begin by saying this: Rarely does a feature that Microsoft doesn’t set on by default mean that it is disabled for a good reason. I still cannot explain why they believe that the repair directory under the SystemRoot directory is readable by Users as a default setting…
Politics aside, you should enable Scavenging for DNS records as long as you are allowing Dynamic entries in your DNS database. Otherwise, a computer that registers itself in the DNS will never expire. Say you set up a test system on your network and never boot it again, the record will remain as long as the DNS database remains without scavenging. You do not need to clean up the database prior to enabling it, but make sure everything is set up properly before turning it on.
See the following site for a description of setting up scavenging: http://www.windowsitpro.com/Windows/Article/ArticleID/19897/19897.html
Hope this helps,