the main advantage is supposed to be a more powerful spark at the plug as it doesn't have to first jump the gap between rotor arm and distributor cap. secondly, you can forget about maintenance of the cap and rotor arm. thirdly, you can use different plug leads, or even install a coil on each plug so that you don't need HT leads at all (if you're clever enough ).

to do it, you still need a phase sensor somehow, so either keep the one in your distributor body (which would be a bit crap), make one to run from the same place, or make one to run from a camshaft (both camshafts and the auxilliary shaft all run at the same speed - i.e. crankshaft / 2, so you can fit a phase sensor on either of them).

then you need some electronics to change the pulsed output from the ecu that normally operates the coil to give an output from each coil. normally you can do this with a second ignition amplifier and run what's known as wasted spark - where you have 2 spark plugs connected to one coil that fires twice in the cycle - one for each time the spark plug that is in the cylinder under compression is ready for it, and one time on one that is in the opposite phase of the cycle (hence the spark is wasted as there is no compressed mixture to ignite).