When creating stencils in one of the 3 formats that Visio uses it can be very important to convert between these 3 formats quickly and easily, ok, there is a Save As command on the stencil toolbar, but what if you have 100 stencils to convert?
Put your stencils into a new folder and use this command to select the stencil input format, then select the folder to convert, then select the output format. The input and output formats can be in VSS/ VSX or VSSX formats.
Note that the VSSX format was not introduced until Visio 2013 so this option is not available for Visio 2010.
Saving in VSX format is no longer available as of Visio 2013 so this option is disabled in version 2013 onwards.
Also note that the output format cannot be the same as the input format.
Warning. If files of the same name and type as the output format already exist then they will be overwritten with no warning.