Q8. Why do some spark plugs have multiple ground electrodes?
A8. This is an attempt by the manufacturers to increase the service life of the spark plug. The ground electrodes can wear down rapidly in some engines. Tiny particles of metal are removed from the ground electrode each time the plug fires hence they gradually wear away. There is a misconception that a multi ground plug will produce mutiple sparks - this is not true, only the nearest electrode to the centre (i.e. currenty the longest) will spark, as that becomes worn, another electrode will become the longest and replace it as the sparking electrode.
Q9. Do my multi ground electrode plugs outperform single ground plugs?
A9. In most cases, no. The additional electrodes disturb the flow of gases around the spark plug tip and performance may even be reduced. In addition, for high performance applications the additional metal within the combustion chamber will retain more heat and may be more prone to detonation/pre ignition.
Makes sense, the more ground electrodes the less space for the air/fuel and flame.