The customer self-billing invoice is not the actual invoice that is posted, but contains information used for creating the actual customer invoice. Additionally, price updates, deviation reasons, and additional self-billing lines can also be managed from this window.
Create Customer Self-Billing
Invoice 
Add Lines 
Update
Sales Part Prices From Self-Billing
Update
Price On Matched Order Line 
Add 
Sales Charges/Landed Costs
Enter Self-Billing Deviation Reasons
Create Customer Invoice
Unmatch or Remove Lines