The switch on the left of the faceplate is a 10 amp switch that can be used for lighting, fans, heaters or any application where a switch was needed.
These outlets were common in bedrooms where only one power outlet was needed, saved running extra wire down the wall. You used a mixed (light/power) circuit and took the active from the terminal on the back to the switch & then run the switch wire (controlled by the switch on the left) back to the light.
