The main reason power lines use high voltage is to minimize energy loss during transmission over long distances. According to the principle of electrical power (P = V * I), for a fixed amount of power (P) to be transmitted, increasing the voltage (V) allows for a significant reduction in current (I). Since power loss in a transmission line is proportional to the square of the current (P_loss = I² * R), decreasing the current drastically reduces energy wasted as heat. This makes the entire transmission process more efficient and cost-effective.