Let me start by saying that I am not talking about the free energy or "overunity" idea of back EMF. When searching around for information I can only seem to find information from free energy sites, which isn't too helpful (perpetual motion and all of that).
With that said, I see a lot EMF suppression and flywheel circuits that take back EMF from an inductive load. These seem to be largely designed to protect other circuitry, but one has to wonder, can't you harvest this EMF, store it in a capacitor for the next cycle? Is there a downside I am not seeing, perhaps the gain is not worth the extra circuitry?