What aspect does a posting key control for each document line item?

A posting key serves as a crucial identifier within the SAP system for each line item in a document, primarily governing how that item is treated in the accounting process. It determines important aspects such as the field status, which dictates which fields are mandatory, optional, or suppressed when entering the line item. Additionally, it indicates the account type that the line item relates to, whether it's a general ledger account, a customer account, a vendor account, etc. Furthermore, the posting type, which is part of the posting key, defines how the financial entry is processed, such as whether it is a debit or credit posting.

By controlling these factors, the posting key ensures that data is entered consistently and correctly, maintaining the integrity of financial reporting and analysis within the SAP system. This holistic approach to line item entry is fundamental for accurate accounting and facilitates compliance with internal controls and external reporting standards.