For those unfamiliar with the app, basically the Groups app seemed to serve the same purpose as Messenger, except that it was dedicated to Facebook Groups. Presumably the idea is that for users who spend a lot of time on Facebook Groups, a dedicated app would allow them to interact with Groups without the distractions from the main app.
In theory it wasn’t the most terrible idea, but we guess not many people saw the need for a dedicated app, which might explain why Facebook would rather devote their time and resources somewhere else. According to Facebook, this doesn’t mean that Groups will be going away, but rather they’ll be spending their efforts at improving the feature within the main app itself.
So if you are one of the few who do use the Groups app, then note that you will have until the 1st of September after which the app will be shut down, so time to start getting used to Groups in the main Facebook app if that’s the case.