The main purpose of a thermostat is to regulate temperature in enclosed spaces such as homes and buildings. It serves as a control device that maintains the desired temperature by turning heating or cooling systems on and off based on real-time temperature readings. Thermostats can be manually set or programmable, enabling users to set specific temperatures for different times of the day. By ensuring a consistent and comfortable environment, thermostats enhance energy efficiency and occupant comfort, playing a vital role in modern heating, ventilation, and air conditioning (HVAC) systems.