Since Excel 2007, Microsoft has split the classical `.xls` format to several formats (in particular, `.xlsx`, `.xlsm`, `.xlsb`). I&#39;ve got no problem to understand the use and purpose of `.xlsx` format but I am still wondering whether we should use a `.xlsm` or a `.xlsb` format when creating a file containing some VBA.

Of course, you can find some topics on the web, for instance:

 - on [Microsoft answers forum](http://answers.microsoft.com/en-us/office/forum/office_2007-customize/personalxlsm-vs-personalxlsb/9e45d7e7-dd27-4541-aff7-6c9b830b4496)
 - on [Microsoft blog](http://blogs.office.com/b/microsoft-excel/archive/2006/07/20/671995.aspx) that was pointed in the previous link (yet I&#39;ve parsed until the 10&lt;sup&gt;th&lt;/sup&gt; page without finding a ref to `.xlsb`)
 - [this topic from another forum](http://www.pcreview.co.uk/forums/difference-betweem-xlsb-and-xlsm-t3299124.html)

What I&#39;ve understood from this last link is that `.xlsm` is some kind of XML format and thus, needed for custom ribbon tab.

Beyond the **conceptual** difference between the format (`.xlsm` is based on *XML* VS `.xlsb` is a *binary* file), is there any **practical** difference when using any of this file (apart from the ribbon customization)?  
Have you ever seen any real difference when using any of these formats?


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When should the xlsm or xlsb formats be used?