Purpose/Functionality of PO Approval Amount (Amount + Nonrecoverable Tax) in Tax Code Summary

When creating a Standard Purchase Order that contains lines associated with a tax code, I am aware that the amount of the non-recoverable tax plus the amount is the Approval Amount. 

However, other than reflecting the approval amount, does this amount serve any functionality?

For example, if my understanding is correct, the Approval Amount is not stored in the database and it does not appear on the output of the Standard Purchase Order (however, we would like for this amount to appear on the Purchase Order). Nor does this amount appear in any of the "canned" reports that came with the module.