Incomplete orders are orders placed by customers that haven't completed checkout. For example, a customer adds a product to his cart but failed to complete checkout due to insufficient funds in his credit card and decided to hold off the purchase. Keeping record of incomplete orders presents an opportunity to lure the customers back via cart abandon email and provides good statistical information to better understand the shopping behavior of your customers. However, as time passes, it may be useful to delete some of these incomplete orders to shrink the amount of data and clutter.
To automatically delete incomplete orders, you must first enable the Sales order feature under Configuration > General. Once enabled, you can enter a value for the Days before deleting incomplete orders under Configuration > Sales order setting. Generally, the number of days should be greater than your cart abandon and session timeout settings to avoid deleting an active customer cart still in progress.
Remember to consider the implications of deleting incomplete orders whether for statistics or tax liabilities. Once deleted, the orders cannot be retrieved.