To emphasize the point, you end up needing to listen to other people instead of having other people listen to you. This is a big problem with discussions, the need to show your own worth easily overrides the value in having an actual discussion.
Another way of looking at it is if people aren't listening to you, it's not a discussion. I was at a small party a week ago, and all 12 people in the room listened to me tell a story. None of them interrupted and felt the need to show their worth. But, I wouldn't call that a discussion.
This is true, though not everyone is worth listening to, and not on $RANDOM subject.
More than 4 people in a hunting party will scare any game. Small groups have evolution advantage.