This is a read-write switch that, per its description, enables the cisgIpsSgTunnelStart notification when set to true, which fires whenever a control tunnel starts - but only if cisgIpsSgNotifCntlAllNotifs is also true, since that master switch gates every notification in this MIB. An admin who wants real-time visibility every time a new IPsec control tunnel comes up, rather than polling cisgIpsSgGlobalActiveTunnels periodically, would enable this alongside the master switch. On a hub that's supposed to have a fixed, known set of spoke tunnels, an unexpected TunnelStart trap firing for an unrecognized peer would be an immediate signal worth investigating.