As with a lot of new features added into Android Nougat, Data Saver Mode was a new feature that was only recommended by Google. This Data Saver feature that Google added to Android does more than just restrict background data usage though. It’s an actual API that allows some applications to continue to function as long as they limit data usage. After reviewing the updated Compatibility Definition Document for Android Oreo, we can see that Data Save Mode is now required for handheld devices that include a metered connection.
On top of Treble requiring the biggest architectural change to Android ever, the engineers at Google have been working to improve battery life as well. They have been easing into this process with Doze Mode in Marshmallow and then expanded this feature in Nougat too. JobScheduler debuted in Lollipop and is now an integral component to saving battery life and keeping applications in a deep sleep mode with the new Android Oreo update.
Google’s goal here is to give Android devices multi-day battery life and this requires certain limitations. On top of the work Google has been doing here, they also want to give more control to those who own an Android device too. As part of the Compatibility Definition Document for Android Nougat, Google had only “strongly recommended” that an OEM include Data Saver Mode on their handheld devices which included a metered connection.
To Google, a handheld device is something like an MP3 player, smartphone or tablet. It is considered handheld when it comes with a power source that provides mobility (such as a battery), and also has a screen size in the range of 2.5 inches to 8 inches. If an OEM releases a device that meets these requirements and uses Android Oreo then it must include Data Saver Mode if it also has the ability to use a metered connection (aka a cellular network).
Source: Android 8.0 CDD