Volvo multi-ground spark plugs - why?

[L.E.V]

Up until now, I have only used single electrode plugs in my 98 S70 N.A..I've used the 2 plugs specified in the manual for the majority of miles on the car which is currently 242k...I've had no issues at all using Champion 344 aka RC9YC, along Bosch 7555 copper core plugs which are made in Germany..back in January i bought Bosch fr7dpp fine wire platinum on clearance from Rock Auto...both throttle response and acceleration is a bit better with platinum plug as opposed to copper but not by leaps and bounds...also my highway mileage is up a slight bit as well...i pour Pennzoil 10w40 yellow bottle along with a Mann oil filter...no issues at all with the new Bosch platinum single electrode plugs nor with the old school copper core plugs...