I recently downloaded a beta test game from the Google Play store and whenever I open it, I get a notification from GmsCompat that says "Missing app: <game> needs the Play Games app" with an "Install button.
The game works fine. I had to log in with my Google account to authenticate the beta invite and it worked. It never seemed to have trouble saving my progress.
The beta is over now so I can't do more experimentation, but I expect I will play the game again when it is fully released.
What does this notification mean? What would I be installing? Since everything seems to work, should I not bother installing it?