Importance of Heat Training

25% of energy created goes to the muscle, while 75% is heat which goes into your blood and circulated through the body, which rises core body temperature, skin temperature & sweat rate. This heat energy needs to evaporate from the skin to cool you down, and thus the energy created by the muscle dissipate into the environment. 
It is important to train in the heat to give your body the chance to adapt to the heat stress the body undergoes when exposed to high temperatures. 

Adding heat training before you know you will be racing in a hot environment helps improve your body fluid imbalances, which will increase sweat rate and the bodies ability to cool your body down quicker. 

As Triathletes we almost must try to be as efficient as possible and try to move long and fast while using energy efficiently.