burbs. Yes this is true. An electrolytic capacitor is a small battery, the only why it can discharge any voltage is for it to be charged and the only way to charge it (in the application we are talking about here) is from the motor and/or battery. When a D.C. motor is being driven, as in when you let off of the throttle and the car is slowing down, it turns into a generator and creates voltage that will help charge the capacitor. When you get back on the throttle, the motor will discharge it just like it does your batteries.
Nothing is free though and there is a catch but it applies more to low turn Mod motors. The larger the Cap that you put on the Speed Control the more it takes to charge it and the little throttle “blip” that is done in the corners will usually not do it. The only way it will completely re-charge itself is to draw off of the source that it is across….the battery. So, you get more punch off the corner with a large Cap because it acts like a very small but extra cell in the pack but in the long run it is less efficient because it has to constantly be re-charged during the run.
In Stock, you hardly ever let off so it doesn't matter. In 19t, the high timing and the occasional “lift” does cause a lot of arcing and I would run a smaller Cap on the speed control, something like 680 Mf. Open Mod speaks for itself.
No matter what your application is, I would recommend the smaller Caps (3) on the motor because all motors are “noisy” with RF and can cause radio interference.