For users who need to monitor data consumption, using data saver options of apps like Google Chrome are useful. Facebook thinks it’s useful enough to try out on its own Messenger app. What the data saver option does is it cuts back the amount of data you use by letting you only look at pictures and videos on a click-to-download basis. This feature gets enabled when you’re on cellular data. If you are on Wi-Fi, the app will continue to download the photos and videos as they come to you. Messenger will also show you how much data you’ve saved. However, the feature isn’t available to everyone yet. But if you’re on Facebook Messenger’s beta program on Android you might be able to toggle this option.
Source: Android Police