A Modano user just asked me my thoughts on using the XLSB file format vs. the XLSM file format, after they read the following article:
http://blog.datasafexl.com/excel-articles/advantages-of-xlsb-excel-binary-format
The big think I pointed out when replying to her is that your choice of Excel file format does NOT affect the calculation speed of Excel once your file is open - i.e. the file format is simply the way in which the data within an Excel workbook is stored when written to file. Once loaded in Excel, a workbook will always behave the same way.
Having said that, we always go with the XLSB file format at Modano because it's the smallest file size on disk and allows VBA macros to be added without having to change the file format, as happens when adding VBA to an XLSX file and being required to then save it as an XLSM file.
FYI - Here's my fully reply to the user:
The Excel 2007-16 binary format (*.xlsb) saves the data within an Excel workbook in binary format instead of Extensible Markup Language (XML) format. Binary (i.e. 1s and 0s) is much more efficient that human-legible XML, so the result is a much smaller file size when saved on disk. However, the choice of file format (i.e. XLSX vs. XLSM vs. XLSB) does NOT impact the calculation speed of Excel once files are open – i.e. it only affects file opening and save speed on a performance level. This is the one thing in the linked article that is incorrect.
So, when considering XLSM vs. XLSB, I would always go XLSB unless for some reason this will cause issues, as the file size on disk will be smaller. But don’t expect any impact on calculation speed once files are open though.