Sending data from the cloud to the app is way more tricky. You want to do it in the most efficient way, to spare bandwidth and device battery life, so you need a way to know what has changed since the last time that specific user and device synced. As data is surely stored in a database of some sort, you also need some efficient method on the database side to make sure you can quickly get everything that is new or changed and that is in the scope for that specific user/device. If your mobile application is successful, this means that you may literally have millions and millions of rows or documents to scan and check for changes.
Not an easy task: all hope is lost then? Just send back the whole data set and that’s it? Of course not! We don’t want to just be developers, but better developers, right?
Modern databases can help a lot in tackling this challenge. Azure SQL, for example, has a feature called Change Tracking that, guess what?, will take care of keeping track of changes for you.
Davide includes a lot of detail and even a sample application on GitHub.