Jaakko Saari has shared a tutorial on how to use Substance in Marmoset Toolbag 3.
Using substance instead of bitmap images it is possible to tweak texture settings on the fly without needing to re-export-import. For things like render backgrounds or floors, this is a great timesaver, but this technique can also be used to preview environmental assets or other models that are later to be used in game engines that support Substance.
Also, check the artist’s new substances on his Gumroad page.