Why do we increase potential difference along power lines

We increase potential difference along power lines so that the current goes lower (p. d up current down). If the current is lower there is less collisions from electrons into atoms, subsequently less energy is dissipated as heat into the surroundings which saves money

The primary reason that power is transmitted at high voltages is to increase efficiency. As electricity is transmitted over long distances, there are inherent energy losses along the way ... The higher the voltage, the lower the current. The lower the current, the lower the resistance losses in the conductors.