Since the release of Excel 2007 it has been storing data as an XML file. This is a good practice if we want to exchange spreadsheets between different platforms, or even operating systems, but when it comes to complex calculations, which contain hundreds of thousands of rows, such documents can take up a lot of disk space. This can be overcome by saving with the use of the XSLB extension. You can read about the advantages and disadvantages of this approach in the text that follows.