AntiVirus profiles within LAN polices ?

Hello, we are currently using flow based AV profiles on all of our 'trust to untrust' firewall policies i.e. LAN to internet. My question is, would you recommend we also add 'AV profiles' to all of our local LAN policies (trusted interface to trusted interface) ? Is this commonly done or is it a recommended practice. I was thinking it might help if a local PC became infected and then spread the infection thoughout the LAN. What is the CPU overhead of adding AV profiles to policies ? Thank you kindly.