It allows the condor_collector process to rewrite all sinful strings that are on the same condor_shared_port server as the collector. Thus, it allows for a completely functional dual-stack service if the entire pool is on the same host and behind a condor_shared_port.
This feature is purposely not documented within the manual as it is a special-purpose and experimental. It is meant for a band-aid in the 8.3.x series before the "sinful string rewrite" is done in 8.5.x.