Explain the importance of the GR/IR clearing account.

GR/IR is an interim account. In the legacy system of a client if the goods are received and the invoice is not received the provision is made for the same.

In SAP at the Goods receipt stage the system passes an accounting entry debiting the Inventory and crediting the GR/IR Account .Subsequently when an invoice is recd this GR/IR account is debited and the Vendor account is credited. That way till the time that the invoice is not received  the GR/IR is shown as uncleared items.