Google Realtime API (or functionality) for Android?

Some questions have already been asked: Is Google RealTime API for Android? and Does the Google Drive Realtime API support Android?

However, it was described by one commenter two years ago as a "high priority" for Google, and I know the Android Drive APIs have increased significantly, however, there doesn't seem to be any Google documentation I can find on topics.

So what are the use cases for the Realtime API or realtime file sharing in Android?