Since too much idler pinching on the filament can flatten it too much to fit through the nozzle, especially with retractions, I thought that by using only one of the idler springs you would cut the pinch force in half and stop the excess flattening. Of course it would still need to be able to pull strong enough from the spool, and push strong enough to get through the nozzle, but for "softer" filaments with lots of retractions, especially on warm days or with lots of rising bed heat, it might help stop jams.