This is very useful for me, because lots of the software I write is SaaS where the customer has their own subdomain - and testing on mobile in a local network is a PITA.

Think of setting acme.example.local and foo.example.local in hosts to 127.0.0.1. In my code I have middleware that sniffs the leftmost part of the hostname and authenticates and routes based on that info.

With this I don't need to mess with hosts, and I don't need to worry about putting in a hack for mobile (on which you cannot change any hosts).