I know that NGK and Densos are supposedly the best plugs to get, but why does my Helms manual say not to use platinums in my 96 LS Integra. The Helms says to use either NGK or Denso Platinums for GSR's, but not for LS's. Also, does non-platinum include iridium plugs?

What are the possible drawbacks of using copper, platinum, or iridium plugs? I know there's price differences, but I once heard something about platinum plugs damaging cylinder heads???

Thanks.