Scenario 

There is a scenario that maybe the supplier is not enough 10QTY of the item and only can delivered for 8 QTY, the customer(User) may just accept it and no intend to follow up anymore, so the user just accept to close the purchase order.

Example: Purchase Order created with 10QTY of ASUS-MB

But Transfer only 8QTY to Goods Receive Note.

there still outstanding 2 unit in Purchase Order

And in Good Receive Note, and Purchase invoice transfer from Purchase order screen, will always remain it still have 2 qty of stock not transfer yet

We can mark as close for this Outstanding Document.

If, we have many same situation transaction, we can mark as close by Batch.

Solution 

To Mark as close for one document.

Click Edit à Click Mark As à Click Closed, and Click Resave.

To Mark as Close by Batch, Click Purchasesà Click Mark Purchase Document Close   Status.

Click Purchase Order Tabà Click Inquiry.

Tick the transaction you want to closeà Click Save.

Result: 

Transaction Closed.

And Outstanding Purchase order no more appear the closed Purchase Order (PO2011/009)

And transfer screen also no more appear the close Purchase Order (PO2011/009).

Same feature is applied into Purchase and Sales Module.