Power BI developers use Data Analysis Expressions (DAX) to create complex calculations and measures that offer deeper insights. DAX formulas allow developers to create custom metrics, perform aggregations, and calculate running totals or year-over-year comparisons. They also use DAX to filter data dynamically and create measures that respond to user interaction within the dashboard. Advanced DAX functions like CALCULATE and FILTER enable developers to perform intricate data analysis, uncovering trends and patterns that aren’t readily apparent. This level of customization with DAX helps businesses gain more targeted and actionable insights from their data.