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.

I found this response: https://community.canvaslms.com/t5/Question-Forum/Setting-A-discussion-so-Students-only-see-their-ow...

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.