When using other containers that have services requiring a vpn to access the vpn in this container, the default iptables config blocks ports and local ips so that services can't be accessed, and if changed it will just reset when container restarts or updates.
Being able to pass ports from the compose.yml file options into the container to open up, or having a config file that is read at startup that has ports to open up or local ip addresses to whitelist would allow other containers with their own services use this container without it being blocked each time.