A: Using create-react-native-app (CRNA) automatically sets you up with Expo. Expo is a third-party client which provides many convenient APIs for common native components like maps integration, etc. React Native init, on the other hand, gets you raw React Native with webpack.
To my knowledge, CRNA is good for making simple or medium-complexity apps quickly, but it locks you in to packages supported by Expo. With regular React Native, you have to spend more time messing with tooling but you get more control and flexibility, and you can develop new native components. CRNA can be a good way to start though, and then eject later.