Utilizing hotter semi-surface spark discharge- It is easier (takes less energy) for a spark to glide along the surface of the insulator than to break through the air gap.
Brisk Premium Spark Plugs take advantage of this feature in its design. Almost 2/3 of the spark travel between the electrodes is along the surface of the insulator. The length of the spark discharge is maximized with only a slight increase in the required supplied ignition energy. The higher voltage buildup at the center electrode before the spark-over results in delivering more spark energy into the combustion chamber.
However, this spark plug requires a sound ignition system (in good condition) for proper operation.