I have always understood that the fruit drawer should have its vent all the way open
— to prevent the ethylene gas from building up and causing the fruit to rot faster — and the veg drawer should have its vent mostly closed to create humidity levels high enough for keeping things crisp. Our vents have numbered dials, 1-10, and we keep our fruit drawer at 8-9 and our veg at 2-3. Veggies can emit ethylene gas too, just not as much as fruit on average, so you don't want that vent all the way closed.
GardenFresh, How Do I Use My Fridge Drawers' Humidity Controls?