When I add people to my course, I see a setting that allows them to interact with students in their section only. I don't know what checking this box would mean since it appears that they would still be able to see the responses of students from other sections within the same discussion.
But the idea, I'd like to suggest is that they make it easier. Yes, you can duplicate a discussion and assign it to a different section only, but ain't nobody got time for that! Please make this a setting within the discussion. I think the person in the forum was a college professor and so his bit about not wanting students to feel overwhelmed by the volume of responses wouldn't apply as much to a high school teacher, but it could. The reason I want to make them stick to one section is so that they get to know each other.