Yeah, another nice use case is using it at your local dev environment where you can use a single lan IP or even loopback IP and have many domains to differentiate your services mirroring the actual DNS hosted version without messing around the hosts file or local DNS server records. Since their subdomains also resolve to local IPs, you automatically get infinite local address subdomains. As long as you don’t mind it’ll resolve via remote name server but they won’t be able to reach back to your local IPs anyway.

Different take but nip.io and sslip.io just let you use your IP as your domain. When you use the hex notation, it’s shorter, more usable and subdomains can just be used at will. Depending your IP address you may even get lucky and get a vanity looking subdomain. Granted it’ll be fixed as long as your IP is not changing. When it does, you gotta switch domains. I’m mentioning this because you said your IP is fixed and I have a similar use with these.