Fat molecules typically contain long chains of carbon atoms. animals tend to store fats for use when food resources are scarce. this is an advantage to the animal because

Answer is: much energy can be gained by breaking the  bonds between atoms in the fats.

Fat, carbohydrate and protein are the three main macronutrients.

Fat molecules contain chemical energy and they are composed of triglycerides.

Fat is the most energy dense, the most efficient form of energy storage and  do not bind water thus do not increase animal body mass.

For example. fat burning in human organism release energy that we use for walking, learning, etc.

if you're asking what comes out, it's steam.