The -dev flag normally sets up Nomad to bind to the loopback interface, which isn’t compatible with Connect. So the -dev-connect is just a helper to make sure that the “dev mode” is configured in a way that will work with Connect: it verifies that you’re running on Linux and as root, and it binds to a non-loopback interface.
If you’re running the Nomad agent in a normal production deployment, there’s nothing special to do for Connect support.