The Save Mosaic Image section contains settings for the digital copy of the final mosaic image that you create in your session.
In the Save Mosaic Billboard Image section you will see displayed information that is determined elsewhere in the application, but is relevant to the file size and output of the digitally saved mosaic, such as Mosaic Size and Mosaic Tile Size. The value Mosaic size on disk will update with changes made to Customized tile width in pixels, Adjust this value to increase or decrease the file size of the final mosaic output. Check Save the mosaic image when completed if you want to auto-save the completed mosaic, and you can also see a the Percentage completed statistic here.
Muse Mosaic saves image data for future reference as you are using the app. In the Image Data Save Method section, choose whether you want image data saved only when the page containing those images has been completed, or if you want it to save per each image.