This is the master on/off switch for the SSG (Service Selection Gateway) subscriber-management feature on the router, turning the whole service-selection/captive-portal mechanism on or off. Because SSG intercepts and redirects subscriber traffic to enforce login and service selection, flipping this to false immediately stops that interception, so every attached host reverts to plain unrestricted routing instead of being funneled through portal or per-service authorization. An admin migrating a broadband head-end off the legacy SSG model would set cssgCfgSsgEnabled to false during the cutover window, then confirm via cssgStatsActiveSessions dropping to zero that SSG is no longer processing any traffic.