Where is the "Rendered Forum Reply" content widget used ?

Question

There is a content widget for thread replies as below in 12.1 
 Can someone please explain where this is used, as for example it is not used in the forum thread widget when rendering nested replies

Former Member · Answer

Search Results, Recommended Content and User Profile Likes and Bookmarks are some of the places "Rendered" widgets are used. Basically they are used in lists that can contain multiple types of content.