This function helps answer the question of how many of a particular item are required to build the end item. An equation is generated for each item which is a multiplication of all of the quantities of each item and their successive parents up to the top level.
Consider this table.
Once the 'Extended Quantity' function is clicked, the equations are written in the first column immediately to the right of the table. The equations are the product of each item, it's parent, it's parent's parent, etc.
In this example, a quantity of 3 'g's are required to build the end item 'a'.