Do you really just follow what others have posted and do not double check with the SAP documentation and even more important with your business needs and some logical thoughts?
In all our >750 plants is a guy who receives the material that is coming in, he compares the paperwork with the goods and then enters the receipt in SAP.
This is the normal and logical process of a receipt in your warehouse.
And now compare this with a 3rd party sales, where the goods are shipped from your vendor directly to your customer.
The warehouse guy does not get any papers from a truck driver, he can't count any goods before he could do something in SAP, he does not even know about this order. And exact this situation is the basis for the standard design: no goods receipt, just invoice.
And any deviation is made because of some special requirements (legal and country specific, or just because of an almighty finance department which can't understand that some of their requirements do not make much sense in logistics. e.g. mandatory 3way matches PO - GR - IR which is not worth the name if you force warehouse people to make theoretical receipts which physically never happened and cannot be verified.