One potential use of for allowing "plugins" in an app (the host app exposes the extension points for others to hook into), where other apps can integrate with that app, within that host app's own views. This is different than existing extensions, which basically only shuffle data mostly one way, and always outside of the app that it is initiated from.

This framework is cross-platform, so it would offer such a plugin architecture on both macOS and iOS.

There's no hints that Apple would offer this kind of integration within their own apps however.