After you create an extract, the current workbook begins using the extract. However, the extract connection is not saved with the workbook until the next time you save. That means, if you close the workbook without saving first, the workbook will connect to the original data source the next time you open it.
You may want to create an extract with a sample of the data so you can set up the view and then switch to the whole data source, thus avoiding long queries every time you place a field on the shelf. You can toggle between using the extract and using the entire data source by selecting a data source on the Data menu and then selecting Use Extract.
You can remove an extract at anytime by selecting a data source on the Data menu and then selecting . When you remove an extract you can choose to Remove the extract from the workbook only or Remove and delete the extract file, which will delete the extract from your hard drive.
You can see when the extract was last updated and other details by selecting a data source on the Data menu and then selecting .