Facebook has rebuilt the Messenger app for iOS from the ground up. The company has been working on a rewrite of the code since last year, and it called this Project LightSpeed. That tells you what the primary driver has been: to make the app faster. And that it is. Facebook says it's twice as fast to launch than it used to be, and it's also just one fourth the size. The company has somehow realized that it's incredibly important for messaging apps to be fast to load, because people don't just open them once or twice a day, but dozens if not hundreds of times. The app is now simpler...
Source: https://www.gsmarena.com/facebook_messenger_for_ios_is_now_twice_as_fast_one_fourth_the_size-news-41791.php
