Your car body is made out of cold forming steel.....something like A36. It has a tensile strength of around 36K PSI. The "normal" weld wire has a strength of somewhere upwards of 60K psi tensile.....this means it's harder on the Rockwell or Brinell scale. Easy Grind is soft....not quite as soft as the body metal, me thinks, but close. It is considerably.....ah... easier to grind which makes it easier to fair into the surounding metal.....and to clean up the mess you've made with your stinger....thas important to me.
It's not too shinney for structual welds tho.