The ancient Aztecs and Mayans added chili powder to hot cocoa for the same reason you might add cocoa powder to a pot of chili [stew]. The flavors of the two ingredients play off one another to intensify the flavors of the dishes. Traditional Mexican mole sauce and American-style chili [stew] are both renditions of the classic flavor combination.
Cocoa powder adds a deep layer of flavor to beans, meat and even tomato sauce. When a dish contains a variety of ingredients or spices, the taste of the dish lingers longer on your palate and offers a complex, as opposed to a simple, appeal. The idea isn't to taste the cocoa itself, but to give the dish multiple dimensions. Always add a little at a time to get your desired taste.
But you can be very creative with this spice, you can use it in your Brownie mix, Chocolate cupcakes, Chocolate sauce, Hot chocolate or Chilli Con Carne to mention a few.
No salt or sugar added, add your own to taste.