A recent visit to Africa by some Facebook engineers prompted them to tweak their Android app. Why you ask? Well, they experienced what it’s like to use Facebook on low-end phones with slow internet connection. They saw how low-end devices crashed trying to load the app and how they managed to consume a month’s worth of data with 40 minutes of trying to use Facebook.
What Facebook did with its Android app was to make it so that it didn’t load everything at once when you opened it. The News Feed entries are loaded much earlier and Facebook images are being transmitted using Google’s WebP format. This means the app loads images in resolutions and sizes based on the device’s screen size. It will only load the full-size photo if you select the photo. The app size has also been reduced by 65 percent to accommodate devices with limited storage and small RAM.
Source: Facebook Code