Looking for some clarification on how AV works?

I ahve a Fortigate 60E setup and enabled AntiVirus Security profile thinking this may do some scans on the firewall (although dont have any UTM bundle for AV) so not sure if this is doing anything? 

Also I have FortiClient on ever PC but only for VPN access - is there a way to stop them scanning as I suspect it will interfere with the paid antivirus we have on our PCs?