In the last few weeks I have spent more time reading articles about what/why/where/ and when you need a ballast then I really care to admit! Pretty much here is what I’ve come up with-
1) if you run points you need the ballast to extend the life of the points regardless of coil type.
2) if you run an ECU (any color) with a STOCK coil (6-9volts) you need the coil manufacturers recommended ballast. The coil will eventually fail/overheat.
3) If you run an ECU (any color) with a PERFORMANCE coil (12 volt) you shouldn’t need one but you should confirm that with the manufacture.
4) If you run a multi-spark ECU you shouldn’t need it regardless of coil type. The coil doesn’t hold the current long enough to cause overheating. Again, confirm that with the manufacturer.

The bottom line here is when you start mixing and matching you have to pay attention to each component’s requirement. Are you going to see any performance gains if you were using one when you didn’t need to, I don’t know but I tend to think the output voltage from the coil won’t be that different but wouldn’t know how to measure that.