Jblake, I must respectfully qualify your statement. It is true that the GM HEI system, which is breakerless, does require a full 12V on the coil. But not all breakerless ignitions need that. The purpose of the ballast resistor is to keep the coil from burning up, also makes the points last longer. If you have a coil that can take the full 12V, go ahead and use it, but most stock coils are not designed for that, and will die. The points, whether mechanical or electronic (e.g. Pertronix) are only there as a switch: when closed current flows in the coil and builds a magnetic field, when it opens the field collapses producing a high voltage on the secondary winding. Unless your coil is specifically designed to run with a full 12V you should retain the ballast resistor, no matter what kind of points you have (mechanical OR breakerless).
I have Pertronix on my dist, with a Pertronix "flame thrower" coil, I use the stock ballast resistor and draw a 2" white hot spark at idle.