dcpcgi is a PCGI handler for Netscape/iPlanet servers. Modern iPlanet servers do not appear to need this, as their CGI handling is advanced enough to be able to call Zope.cgi directly without a performance penalty.
However, this will utilize the pcgi pipe in Zope to transfer requests from the Netscape/iPlanet server to Zope.
Tests in June of 2000 indicated no noticible improvement with iPlanet Server 4.0, but Netscape FastTrack Server did improve to iPlanet Server 4.0 speeds (about 5% slower than native Zope).