Heat reduces the surface pressure of water, allowing it to clean faster and more professionally than cold water. In fact, the heat in hot water triggers the movement of chemicals working during the cleaning, which makes for easier soil removal from synthetic carpets.
Cleaning carpets with hot water will drastically improve productivity, and reduce residue being left behind by other cleaning methods.
Heat also works well with spot removal in addition to rinsing the carpet. Spots are soils and additional heat will work wonders. The same concept is used in your dishwasher. The hot rinse removes any lingering residue allowing for clean spot free dishes and the same is true for carpet.