I’ve used it to open a local port on my laptop publicly without needing to make any changes to the local network I was on. It can be useful for opening your laptop’s ssh port or to host an http server to send someone a big file you don’t want to pay to upload somewhere.
One other common use is 🏴☠️ which I suspect is why they disabled the service :/
Sounds like OP is gonna flash OpenWRT… Did you read the post?