The void does not conduct heat, while any starship constantly produces it. Therefore an efficient system for radiating off the heat is needed for long space voyages to prevent the crew from cooking alive. Traditional radiators are impractical due to their huge size. The solution is to have coolant dispersed into fine mist around the ship, trapped in a forcefield and kept circulating. As the surface of radiator decreases relative to fourth power of its temperature increase, it's best to keep it as hot as is bearable.