Enabling this feature allows your site visitors to respond to news stories. Imagine a newspaper where letters to the editor appeared immediately and under the appropriate news story. Make it electronic and you have a good idea of how News and Comments relate to each other.
In practice, they function much like a forum program that offers a choice of message threading and a choice of different moderation types.
Note: Comments also appear for the Reviews module and are enabled by default. However, they are not controlled by the settings in this section.