Port following is set when two services need to share persistence records. Typically this is done for HTTP and HTTPS services so users maintain a server session regardless of whether they connect securely. This is explained in our manual in Section 4.6 and 16.7.
Port Following does have several requirements:
After meeting these conditions, there will be an option under Advanced Properties for Port Following. Be sure to set this on both services to ensure that port following is done bidirectionally.