actual need for ballast resistor with electronic ignition?

Short answer: Ma Mopar's first take on an electronic ignition was back when "This design uses one less transistor!" meant major cost savings instead of ten cents per part. So it's a very simple design. The module behaves like a closed set of points until it gets a pulse from the distributor pick up. Then it "opens" to fire the coil for a few milliseconds before "closing" until it gets another pulse.

So, if you turn the key to run without the distributor turning, the ignition box will just act like a closed switch. It would just run all the current through waiting for a pulse that never comes, and get very hot in the process. So you put a ballast resistor inline to hold the current and heat to reasonable levels.

More modern ignition modules "keep the points open" until they read a signal from the distributor and adjust the dwell to limit current.