For electrical outlets that have on/off switches, is energy sent to the socket when nothing is connected to it but the switch is on?
A switched outlet with nothing plugged into the outlet will generally not consume any power when the switch is turned on. There are a few cases where this may not be totally true. Some outlets may have an indicator to show that the outlet has a live power connection and the indicator circuit will consume a small amount of power.

Some indicators would be a neon bulb, others LED and some may be small incandescent bulbs. Each type will consume a small but different amount of power.