Here are some good reasons to choose Big Fat Spark together with 123ignition when operating multi cylinder engines.

123ignition for high-performance ignition modules generally needs a relatively high resistance in the primary windings of the coil. The high resistance limits the electrical current flow to a degree the 123ignition can handle. If the resistance is too low (and therefore the electrical current flow too high), the electronics of the 123ignition either cuts off the current flow (protective circuit) or if the current is only slightly too high, the 123ignition will behave strangely giving non-consistent ignition values (ignition timing bouncing around 10-15 degrees).

Coils with relatively high resistance, used to counteract this sort of problem, have the big disadvantage of having a relatively long charge time. Engines with 4 cylinders revving in a normal range normally do not experience problems however engines with more cylinders or engines using higher revs may experience problems.

Example: Ignition occurs 10,000 times per minute in a 4 cylinder engine revving 5,000 rpm, i. e. 167 times per second. This means the coil will have to charge and discharge at the same rate. A 6 cylinder engine revving with the same speed needs a coil charging and discharging 250 times per second, an 8 cylinder engine 333 times per second. 

Due to the high resistance (and the subsequently resulting long charge time) the coil will not be completely charged which will result in the coil being unable to spark with its full power. The result is at high revs peak energy cannot be provided when it's most necessary, resulting in misfiring, weak performance, unclean combustion gases and high consumption.