Saving an Excel File as XLSB Dramatically Reduces Size
While we hope you never have to deal with Excel spreadsheets large enough to worry about file size, you may find yourself in the situation at a future desk job.
Saving an Excel document using the XLSB format will reduce the size of the file while maintaining full functionality. The XLSB file type stores data in binary instead of XML, making it a faster format for working with large spreadsheets.
XLSB only works out-of-the-box on 2007 or later versions of Excel, but downloading the Microsoft Office Compatibility Pack will allow you to work with the format on older versions.