On theory, this method is the best method, since it relates the ending inventory goods directly to the specific price they were brought. However, this method allows management to easily manipulate ending inventory cost, since they can choose to report that the cheaper goods were sold first, hence increasing ending inventory cost and lowering Cost of Goods Sold. This will increase the income. Alternatively, management can choose to report lower income, to reduce the taxes they needed to pay.
This method is also very hard to use on interchangeable goods. For example, it is hard to relate shipping and storage costs to a specific inventory item. These number will need to be estimated, and hence reducing the specific identification 's benefit of being extremely specific.