If you think about it for more than 2 moments you will see that owning Giphy allows Facebook to see which chat apps you're using (via the api key for the app's Giphy integration) and who you're talking to on them (by attaching an id to each gif similar to how tracking pixels work in email.) Most chat clients automatically load images, triggering the tracker.

This gives Facebook unprecedented visibility into the user counts, usage patterns, and social graph of any chat app with a Giphy integration. These apps compete with Facebook's own chat apps.