Implementing an active-active firewall cluster stretched across separate pods with anycast services configured offers several advantages, one of which is that it allows for optimized routing within the Cisco ACI fabric.
When anycast services are used, each pod can have its own anycast node (firewall instance), and due to routing preferences set within ACI's spine switches, they will prefer their local pod's anycast node for routing decisions. This preference enhances efficiency by reducing cross-pod traffic and improving response times since local spines direct traffic to their respective local pod's anycast nodes. References: Implementing Cisco Application Centric Infrastructure Official Cert Guide