DNS scavenging can be useful with respect to domain controllers because you do not want a domain controller that is no longer around (or perhaps has been moved, or maybe no longer covers that additional site using autositecoverage) to continue to have SRV records advertising that it is still available. This would lead clients to try getting services to it when they no longer could or should. That could lead to errors or latency at best on the client side as you might end up seeing a client in Chicago get authentication, for example, from a domain controller in New York. Scavenging can help remove that record if it should no longer be there, based on the last time the DC that record represents tried to register it. In other words, if it’s old it will be removed.