One advanced technique for optimizing data refresh times in Power BI is to leverage query folding. This is a process in which Power BI pushes as much of the data transformation and filtering logic as possible back to the data source. By doing so, Power BI can delegate these operations to the source system, reducing the amount of data brought into the query engine. Another technique is to create incremental refresh policies, which allow you to only refresh the portion of data that has changed since the last refresh, rather than refreshing the entire dataset. Additionally, optimizing data models by removing unnecessary columns, using appropriate data types, and creating relationships wisely can also significantly improve data refresh times.