This reports the type of identity - such as an IP address, FQDN, or distinguished name - this device used to authenticate itself to the peer for this specific Phase-1 control tunnel row, per its description. It matters because, as with the device-wide cipsIsakmpIdentity object, an identity-type mismatch against what the peer expects is a common cause of authentication problems, and having it per-tunnel lets an admin verify the actual identity type used on each individual connection rather than assuming device-wide consistency. A tunnel showing 'fqdn' when the peer's config expects to match by IP address would explain that one specific connection's authentication trouble even if other tunnels on the same device work fine.