Actually no - you have two choices. Let's say your right foot is forward, pressing down. You can passively let the left foot rest on the pedal as it rises, so your right leg is doing all the work on pushing your left leg up. Or, you can pull up gently with the left leg, just enough to lighten the load on the pedal without losing contact.

In either case, you are not wasting energy. Some force has to lift the left leg. It can either be the muscles of the left leg pulling up, or the muscles of the right leg pushing down. As long as you are not actively resisting the upward motion, it is the same amount of work either way.