Generally, modern ignition systems are pretty good to begin with. The stock ignition systems in our Honda/Acura cars can easily handle most bolt-on modifications. However, when modifications resulting in a lot more air and fuel going into the engine, the spark requirements may start to tax the ability of even these good stock ignition systems. When turbo/NOS is done, aftermarket ignition systems almost becomes a necessity unless you desire big holes in your engine due to severe detonation.

Aftermarket ignition systems use a capacitive discharge system which allows a consistent and powerful spark. In modified cars with more air and fuel, the powerful spark allows more complete combustion which yields better fuel efficiency, power, and smoother idle.

From: Jeffrey Ho-See
For max spark power, you want a (1)big spark in a (2)short amount of time. A good ignition box will do both.

No matter how awesome your ignition system is, it's always limited by the resistance it has to travel. The final say is the plug itself. The bigger gaps need higher voltage for the spark to jump. There is a point of diminishing return of course.