Final answer:
The document type in accounting controls which account types and posting keys are allowed for postings.
Step-by-step explanation:
The document type in accounting controls which account types are allowed for postings. For example, an expense document type may only allow postings to expense accounts, while a revenue document type may only allow postings to revenue accounts.
Additionally, the document type controls which posting keys are allowed for postings. Posting keys are numerical codes that determine the nature of the transaction, such as debit or credit, and the account type being affected.