Power BI developers are skilled at optimizing performance when working with large datasets by utilizing best practices in data modeling and query optimization. They reduce load times and improve report responsiveness by implementing techniques such as query folding, data aggregation, and incremental data refreshes. Developers also optimize data models by creating efficient relationships between tables and using DAX functions to minimize computational strain. These optimizations ensure that even with massive datasets, Power BI reports remain fast, scalable, and capable of delivering insights without lag or performance issues.