If you use the Inventory Management option in Woocommerce, each order will decrease the stock level for products, depending on what quantity of the stock was purchased. However, when you wish to refund an order or when a customer cancel an order, the stock level will not increase and the shop manager needs to manually restore the stock on the product or order admin pagea.
Automatic re-store of cancelled/refunded orders could save you time specially when you run a big woocommerce store with large inventory and/or when processing large number of orders.
WooCommerce Auto Restore Stock will automatically restore your WooCommerce inventory/stock for refunded or cancelled orders. The inventory/stock restore is triggered when the order goes from on-hold, processing, completed to either cancelled or refunded status. When WooCommerce Auto Restore Stock restores the inventory/stock it will also add order notes to the order in question to show the adjusted values and to indicate that inventory/stock was restored.