In the fiscal year 2023, Walmart Inc., a multinational retail corporation, reported net sales of $550,000. At the beginning of the year, Walmart had an inventory worth $80,000, and by the end of the year, the inventory increased to $90,000. Calculate the cost of goods sold (COGS) for Walmart Inc. during 2023. Provide a detailed explanation of the calculation process and discuss the significance of COGS in evaluating Walmart's operational efficiency and profitability.