After a packet has been allowed by the Security policy, Security Profiles are used to scan packets for threats, vulnerabilities, viruses, spyware, malicious URLs, data exfiltration, and exploitation software.

When the destination NAT translation is selected as Dynamic IP (with session distribution), the firewall uses a round-robin algorithm to distribute sessions among the available IP addresses that are resolved from the FQDN. This option allows you to load-balance traffic to multiple servers that have dynamic IP addresses1. Reference: Destination NAT, NAT, Getting Started: Network Address Translation (NAT).