Either the vendor transaction will not be dated with the invoice date, or the value of the inventory will be updated retroactively. If you select this field, the vendor transaction and associated tax will be dated with the specified document date, and the inventory value will be updated with the specified invoice date (date of update). To secure the balance on the date in the General ledger module, the Purchase offset account is used to post the difference between the two dates. The balance of this account will therefore show an accrual between the Vendor and Inventory module regarding the purchase invoice. If you do not select this field, all the updates regarding the invoice will be carried out on the specified invoice date. Any document date specified will instead be saved in vendor transactions and in the invoice journal.