What is a GR/IR account? Why is it maintained?

A GR/IR account represents goods receipts and invoice receipts. This is a clearing account that is maintained to nullify the time difference between goods receipts and invoice receipts from the business partner. The balance in the GR/IR account increases because of the following:

•  If the quantity received is less than the quantity invoiced. The system then expects further goods receipts for this purchase order in order to clear this balance.
•   If the quantity received is more than the quantity invoiced. The system then expects further invoices for this purchase order to clear this balance.