SKU is helpful to maintain inventory system of products and management knows stock level by product SKU, Like the product inventory product options are also need to track, in default OpenCart there is no way for that, thus product option SKU module comes. Using product option SKU, store owner can add/edit SKU for each product options and maintain inventory for options too. SKU will help to easily locate and pick up the right options for products. Product option SKU will show on almost all places where product options show, like product page, mini cart, cart page, checkout page, order history page, admin order view/edit page. SKU is recording when order gets placed with product options.