Power BI development responsible for optimizing report performance by improving data models, using efficient DAX calculations, and reducing dataset size. They remove unnecessary columns, aggregate data where possible, and use techniques like DirectQuery or live connections for real-time data without importing large datasets. Developers also analyze report performance using Power BI’s Performance Analyzer tool to identify bottlenecks and make necessary adjustments. Efficient report design ensures faster load times, smooth user interaction, and scalability, particularly when handling large data volumes or real-time updates.