It is common in some industries to receive less than ordered from the supplier to a tolerance and consider the PO fulfilled. At current you have to adjust the PO line down to match the receipt quantity. In doing so you no longer have the ability to track the vendor performance on the minus side. The 2020 Wave 1 (finally) takes care of the plus side but not the minus side. Ideally you would want to be able to:

1) close the PO without having to adjust the original PO line (either automagically or by user putting in shortfall on PO line.) If all lines on PO are balance from an over and under perspective then the PO will be considered closed.
2) retain the original PO amount and the amount short so that you can run a vendor performance report to be able to see if he has been consistently under shipping and not just over shipping. It isn't just about the payables aspect. It is about metrics to manage your vendors performance.