FortiClient - Security Fabric

It appears that the Security Rating in the FortiGate prefers that computers have FortiClient installed. I know that there are both free and paid versions of FortiClient. Can the free version of FortiClient be used in the Security Fabric to increase security or is the free version only useful for SSL-VPN or IPsec VPN connections? If it requires a paid version of FortiClient, how beneficial is this in preventing real world security challenges?