Ridge vents installed without baffles permit the wind and elements to come right through the vent. As air comes in, pressure can build in the attic, keeping moisture and air trapped in there. The humidity that gathers in the attic can cause damage over time.
A ridge vent with an external baffle does not bring wind inside the attic, as the baffle knocks wind up and over the top of the vent and in so doing builds enough pressure to start drawing air out of the attic. This keeps snow and rain from blowing into the attic through the vent. Also, having a weather filter inside the ridge vent keeps snow, rain and bugs from entering the roof, giving the attic a more reliable barrier against the weather.