Running our app on a simulator/emulator is a very reliable way to feel how our app will behave in a mobile device. We can simulate touch gestures, poor network connectivity environments, or even memory problems, when working in simulators/emulators. But eventually, we would like to deploy the app to a physical device, so we could perform a more in-depth testing.
There are several options to install or distribute an app built in React Native, the direct cable connection being the easiest one. Facebook keeps an updated guide on how to achieve direct installation on React Native's site (https://facebook.github.io/react-native/docs/running-on-device.html), but there are other alternatives when the time comes to distribute the app to other developers, testers, or designated users.