I agree with this. The only vm I have that has multiple interfaces is an opnsense router vm heavily optimized for kvm to reach 10gb speeds.
One of the interfaces beyond wan and lan is an interface that links to a proxmox services bridge. It’s a proxbridge I gave to a container and is just a gateway in opnsense. It points traffic destined for services directly at the container ip. It keeps the service traffic on the bridge instead of having to hit the physical network.