Imagine that you have several products in your inventory that are physically absolutely the same products.
Eg there is an "English Breakfast" tea and "Breakfast in England" tea which are absolutely the same inside and have the same price. Only package labels are different.
And our customers don't care which of them will be actually delivered.
By default if there in not enough stock of the "English Breakfast" available you will not be able to complete the operation even if you have enough stock of the "Breakfast in England" available.
This module provides a solution for such case by allowing to substitute one product with another in the inventory operation.