What if you live in a college dorm or use apartment wifi where they do not give you control of the port forwarding rules? Or what if you want to deploy devices into other peoples' networks (e.g. IoT)? What if you're sending someone a bootable USB image so you can do data recovery on their hard drive in situ without them having to ship it to you? What if you're behind a carrier-grade NAT and don't have a public IPv4 address at all? In these cases and many more, you might find a wireguard bounce host useful.