In Which Car You are gonna use it.....!
Usually Ballast Resistor Is Need In Point Type Distributor Systems To Reduce Wear On Ignition Components + Also Makes Engine Starts Effectively by Doubling The Voltage When Engine Is Being Cranked....!
So If Originally It Exisit On Your Previous Coil....Do Use It..And Make Sure Its All Ok.....!
And Yeah I Am Using Same Bosch Coil From Last 3 + Years...!Its Working Awsome And Have No Complains Yet..!
Regards