Again this depends on the scenario, and real-time events and chats are different.
What you see in my screenshot is a goal scored in a hockey game. A bad goal for our team --> It ignites a strong community reaction of “WTF just happened”.
In real time events the number of people is relatively static. It may increase or decrease gradually, depending on the quality of the event. Now, if something significant happens within that event, it sparks a response like seen in that shot.
Now if you see that there are 20 inbound responses and you are about to say something insightful, this indicator helps you to time your response.
As said, the current implementation has been praised. Just a little UI glitch. Personally I did not think too much of this new feature until I saw it live in our production environment.