How important is intake ventilation as part of an overall attic ventilation system?

Here is some information about the importance of intake ventilation.

Intake ventilation is very important for all types of exhaust vents. Each attic should have an equal amount of intake ventilation low at the roof's edge or in the overhang or undereave and exhaust ventilation at or near the peak of the roof. This is known as a balanced ventilation system. If there isn't enough intake ventilation, for example, a ridge vent (one type of attic exhaust vent) can pull air from one side of itself right out the other side. Picture a wave going into the vent and right out. The problems with ridge vents pulling air in one side and out the other is that it will only be ventilating the very peak of the roof instead of the entire underside of the roof deck. Furthermore, it could bring into the attic precipitation from outside.