Extract filters remove data from the extracted data source. Simply put, the data isn't there. Thus, performance is enhanced by reducing the overall amount of data. Performance may also be improved since extracted data uses Tableau's proprietary, columnar dataset. Furthermore, extracts are always flattened, which will have performance advantages over connecting to datasets using joins.
To create an extract filter, begin by selecting Data > [Data Source] > Extract Data. In the resulting dialog box, choose to add a filter.