Mohamed Said peeked behind the curtains and explains on his blog how Laravel Valet works behind the scenes.

The idea behind Valet is that it configures PHP's built-in web server to always run in the background when the operating system starts, then it proxies all requests to a given domain to point to your localhost

If you want to keep Homestead around for some projects, know that your can also use dnsmasq to point an entire domain to your Homestead installation.