Mobile application development consists of two main things coding and debugging, coding can be done with any code editor but debugging needs some resources so we can say that when you have good testing or debugging environment then only you can make the development process easy and fast. Generally, we use Android Emulator / iOS simulator or real device for mobile application development but for React Native mobile app development Expo has taken it to the next level by providing a very interesting Expo Snack.
I personally will recommend using this for the primary development or for the designing related things as it runs online and can help you to develop the application faster. It uses the Expo environment so I suggest not to depend on it completely as you have to eject from the Expo environment for the final build. You can find the Expo Snack below.