The COUNT function in SQL is used to determine the number of rows in a table or a subset of rows that meet specific criteria. When combined with the CASE WHEN statement, you can count rows based on conditions, creating custom categories for analysis. This is particularly useful for analyzing data that has different categories or states. For example, you might want to count the number of orders for different product types or the number of customers in different regions. The CASE WHEN statement allows you to define these categories dynamically within the COUNT function. This approach is more flexible than using multiple COUNT statements for each category, as it allows for a single query to handle multiple conditions. It's also more efficient, as it avoids redundant calculations. The result is a concise and powerful way to aggregate data based on specific conditions.