"And the C's said that yes, it grounds the flow and gets the engine running. But I don't understand, and what I can't fix into the idea, is why would it slow the planets down?"
As far as I can tell, this hasn't been answered yet. So, perhaps looking at it from a slightly different perspective may help. First - "it grounds the flow and gets the engine running": Think of current flowing in a wire; the two leads are connected and you have power. Second - "why would it slow the planets down?": Well, instead of thinking of it as an engine or motor, try thinking of it more like how generator works. Two magnets creating a magnetic field and a coil of wire spinning in between them which causes current to flow in the wire. With a generator, when the current starts flowing in the wire the coil becomes harder to turn; it creates resistance. In some generators, the coil is stationary and the magnets rotate. In the Solar System, the sun and its little brother have the current flowing between them just like the wire and the planets are the spinning magnets. Still, the same kind of resistance would be created which would slow the rotation. Of course, in the Solar System, there is more involved i.e. the sun spinning, the companion in orbit, the magnetic field on the planets decreasing, and the sun's gravity increasing. However, breaking it down to the most basic concepts, by explaining it this way, its a little easier to understand, OSIT. I hope this helps.