Otherwise known as Raw Sugar, Demerara sugar is about 97% sucrose, so most of it will ferment out, and will not impart much to the body of your beer. Generally used in darker beers, as the light brown color of the sugar will affect the color of your beer.
Perfect for darker beers that could benefit from the slight molasses flavor. I found it did not impact major coloring on the amber beer wort. Slightly larger crystals vs. Turbinado so I would recommend dissolving in only warm/hot water.