This is a master on/off switch: per its description, any specific notification defined elsewhere in this MIB module is only actually enabled if both this master switch and that notification's own individual control object are set to true - the two conditions are ANDed together. It gives an admin a single point of control to instantly silence or enable every notification this MIB can generate, without having to individually toggle each of the specific control objects like cisgIpsSgNotifCntlTunnelStart. Setting this to false during a planned mass-maintenance window would suppress every IPsec-signaling trap from this MIB regardless of how the individual notification switches are set, then flipping it back to true afterward restores whatever granular configuration was already in place.