Backing up data and files in Android is not exactly a walk in the park. It is not easy especially app backups. What happens is when you want to delete a mobile app, all its content will also be erased forever. It is an easy way if you want to clear up your device but for important messaging apps, there may be times that only want to keep the messages and other data.
Link: Keeping app data possible with Android 10, WhatsApp now does it