You will need DJI Go anyways, even if you are preferring flying with Litchi.
1. Available updates will only show up and install while using the GO app, so you should run it at least all few days for firmware checking. And remember, if you have several batteries you should run the GO app with each of them after doing a firmware update, to ensure that all batteries are updated, too.
2. Some Mavic settings and calibrations can only be done from within the GO app.
3. Some special functions, such as tripod mode are only available within the GO app.
Try with GO 4 and only go back to GO 3 if you will run into problems with your mobile device.
The apps will co-exist on your mobile device, but you cannot just exit one app and start up the other while being connected to the remote, alt least not with Android devices. If you want to change the running app you will have to exit the app, then unplug and replug the USB cable and finally start the other app.