This avoids cost inaccuracies that can result from incorrect calculations of production levels and the amount of fixed cost per unit. Calculating variable costs shows the profit after all invoices have been paid for the period. Some revenue will not be received for products still in stock, but when those products are sold, the business will reflect the excess revenue. Profits not affected by inventory changes. According to many opinions, variable costing is the best system to use to manage cash flow and managers find it more.