Instruction: Describe how you would use Excel's 'SUBTOTAL' function to analyze a dataset containing sales data by region and product category.
Context: This question evaluates the candidate's ability to use Excel's 'SUBTOTAL' function for sorting and summarizing data. Candidates should demonstrate an understanding of how to apply the function to specific scenarios such as grouping data by certain criteria and calculating aggregated values like sums, averages, or counts, which are essential for effective data analysis in business environments.