It gives you energy

When the diet goes out of the window, you can do much worse than snack on a piece of chocolate. Chocolate is an energy food, high in carbs with a low GI, and provides the body with instant energy to give you an effective and long-lasting pick-me-up. 

What's more, chocolate contains the tonic substances caffeine, theobromine and theophylline which have a stimulating physical and psychological effect. Fantastic for sportspeople and for anyone after a quick energy hit on the hoof.