SharePoint Discussion Column is a custom column to record users' discussion when they edit the item. Discussion records can be listed in chronological order with discussion contents and discussants' names.
With SharePoint Discussion Column, you don't have to choose "create version each time you edit an item in the list" when you want to select the "Append Changes to Existing Text" option of RichText column.
SharePoint out-of-box Multiple lines of text column provides an option "Append Changes to Existing Text" to let users append their own comments and discussion without replacing others'. But it has two defects. First, you must enable version creation when item edited, but it is not a good solution when you don't want to create new version every time you append changes. Second, every time you edit the item, a new record will be produced in the record history of this column, no matter whether the input content is empty or not. It is inconvenient for users to view a lot of records with empty contents. SharePoint Discussion Column solves these problems - you don't have to create new version when append record and it does not display empty records.