If you use FTP and require the ability to resume file transfers and your sitting behind a Fortigate appliance, you will probably want to create a rule specifically for FTP traffic without AntiVirus rules. If you do not disable AntiVirus, you will get an error like "502 Command REST not allowed by policy".
If FTP resume is required and can be restricted to a certain destination host, or a group of destination hosts, then that is preferable to leaving it open to all destinations.