Ventilating the attic is a good thing because of the heat gained by the air in this space by the sun light baking the roof above.  If the temperature in the attic is higher than the ambient outdoor temperature then ventilating it would be beneficial.  Heat is transferred by convection, conduction or radiation.  Things that aid in heat transfer away from the living space, or minimize heat transfer into it will be good things in general.  Most convection, the movement of material is hot air moving upward, not down from the attic to the house unless pressure differences occur (why top opening freezers tend to be more efficient).  Conduction is a function of the cube of the temperature difference if I recall correctly, so minimizing this would be beneficial, which means that cooling a hot attic would be to some extent beneficial in this regard, and keeping surfaces cooler means that they will radiate less energy as well.