Metallic (Sintered) pads last longer, handle heat better, and resist fade better under heavier braking loads, making them extremely good for downhill rides. In wet conditions, metallic pads are a must, however they tend to be noisier in the wet than in the dry.
Guide trail brakes are designed to slow you down in a hurry, and nothing contributes to that more than the pads. Perhaps that's why few would argue that there is a special joy one feels when they know their bike is equipped with a set of pads that allow you to control yourself on the steep stuff without them over-heating or failing.
