Answer
Since fats are excellent stores of energy, the body would store them either when excess energy was available, when one's diet is too rich, or in preparation for a coming hard time such as during autumn to hold onto calories for the winter.
Work Step by Step
The key here is to see the role of fats in storing lots of energy in a small space. You should then try to imagine circumstances under which the body would try to store a abundance of energy.
