The upshot is that your body has a preferred softness or rigidity of the lower limb. Controlling the limb stiffness is how the body controls excess motion at the center of mass (how much your torso bounces around as you run).

If you put on shoes that make the limb behave as though it is too stiff, the body will try to soften the limb even more to counteract it. If you put on shoes that make the limb behave as though it were too soft, your body goes into overdrive trying to make the limb more rigid. Both compensations waste energy and stress tissues.

Posture matters much less than sense of effort and comfort in motion. If you put on a pair of shoes that make you feel like you are flying, those shoes are working with your "zone of optimal limb stiffness" to make you more efficient than the pair of shoes that feel like wobbling and wading in marshmallow or the pair of shoes that feel like stomping in hiking boots.

Buy shoes that make you feel like you're flying.
Buy OTC insoles that feel as good to your feet as your best bike saddle does to your butt.