How did the double action steam engine affect economy?

In a single action steam engine, high pressure steam is introduced into a chamber formed by the cylinder and the piston. The steam entering the cylinder has two jobs to do:

1. Push the piston down in the cylinder, which turns the crankshaft, and so provides mechanical energy for powering a locomotive or steamship, or doing other useful work,
2. Overcome the frictional loss, mostly of the piston rubbing against the cylinder wall as it is pushed down by the steam and then returned to the top through the inertia of the flywheel. This effort does not provide any useful work and is considered wasted energy.

In a double action steam engine, once the steam in the cylinder has pushed the piston down to the bottom of the stroke, additional steam is introduced at the other end, which pushes the piston back up to the top of the stroke.

The result is that there are two power strokes, but only the same frictional energy loss as in a single action steam engine. In effect, you have cut the frictional loss in half for each power stroke, and this increases the efficiency of the engine, and therefore also increases the fuel economy of the system.