Private chats with any player in the game.
Group chats for tracks, teams, and pretty much any players you add to the chat.
Much more, as in there are more possible uses for group chats and private messages. For example, Division group chats, state group chats. Also, you could message moderators if you need help. It's a lot easier for players to message in-game than to sign up on the forums and create a post.
Another idea is to have the ability to block other players. This way, if they are annoying you or causing trouble, you won't receive their messages.