A low temperature thermostat reduces the temperature at which cool water mixes with warmer engine temperatures. It allows the engine to circulate chilled water sooner than a typical thermostat does.
Some people have a misconception that a low temperature thermostat makes the engine run at a cooling temperature. However, the determining factors in temperature are the engine load and the cooling system. Even if the low temperature thermostat allows earlier circulation, if the coolant can't remove heat, then the engine still runs hot. People thinking that a low temperature thermostat boosts cooling performance and overall power are laboring under a misconception.