Open item management means that a line item needs to be cleared against another open item. At a particular point, the balance of an account is the sum of all open items of that account. Generally, you make these setting in the G/L Master for all clearing accounts, such as a Goods Receipts and Invoice Receipts [GRIR] account, customer account, vendor account, or bank G/L account, or all accounts except the main bank account. Open item managed accounts always have line item management. You can switch open item management on and off through transaction code FS00.