Muscovado sugar is mostly used as garnish because of its characteristically bigger granules. When you want your pastries, cookies, cakes finish with some extra crunch, extra color, and a bit of sweetness, use it as topping. Best for plain cookies, scones and muffins. This sugar does not melt easily, thus, don't use in place of regular sugar.
I think you are referring to demera or turbinado sugar. Those sugars have large crystals. I worked at a bakery and that is the kind of sugar we used to top our ginger cookies and it had a crunch to it after coming out of the oven.