Expense Items without Receipt - Accouting Impact

Hi,

1. We are using encumbrance for both Requisition & PO

2. We have both Inventory Expense(Inventory Flag: Y, Costing Enabled:N) and Expense Items(Inventory Flag: N, Costing Enabled:N)

3. Inventory Items set to - Accrue At Receipts and Expense Items set to - Accrue at Period End.

My Question: Users are not creating Receipts for some Expense Destination POs and Directly matched the Invoice with PO and process the payments.

                      What is the accounting impact if there is no receipt created in the system?

                      If there is the impact, what is the way to achieve this functionality(Match the invoice with PO without receipt creation)  without any accounting impact?