I believe platinum is used to prolong the time between plug changes. Platinum is very superior to copper in terms of corrosion and erosion in the combustion chamber environment. However I believe copper plugs use a large diameter copper electrode to carry power (copper is dirt cheap.) Platinum (expensive metal) plugs use much smaller diameter tips and are not able to carry as much power. Dose the power (length of spark is function of voltage) make that much difference in your car? I do not know.