The purpose of this feature is to give users quick access to information without having to open an item. For example, they are on an Accounts Display page and the associated Sub Grid displays an Opportunity. In the Sub Grid there is limited room to display all the details of the Opportunity so the Quick View will give access to additional information which may in many cases prevent the user from having to open the Display page for the Opportunity.
This function can be added to any list. Once added to the Advanced Settings for specific lists the values will display in all Sub Grids for that list.
Add the following setting for every list you would like to add the Quick View to.
Setting Name: [ListName]SubGridQuickViewColumns
Setting Value: A list of column names