The sugar in Brown sugar is 100% sucrose and 100% fermentable, so it won't add sweetness to the batch. The molasses in the sugar will add new flavors.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk