If you leave your kettle plugged into a wall receptacle does it waste electricity?

No as the circuit is broken so no electricity can flow through the ciircuit

.

<<>>

Most small appliances these days have switches on them. The voltage potential is at the kettle but stops at the switch. As soon as the switch is turned on, the circuit is completed and the appliance operated.

In the UK there is a switch combined with the receptacle. This switch is used to disconnect the voltage output to any device that is plugged into the outlet.