Purpose of low-humidity crisper? My refrigerator has two crispers, with humidity sliders from low to high. A high-humidity crisper is pretty easy to understand: it traps the moisture inside, preventing leafy greens from wilting. On the other hand, when you slide it to low humidity, a vent opens allowing air to pass through. How is that any different from storing food outside the crisper?
If you set it to high humidity (no air flow) and add plenty of water fruits, f.e. water melon halves, then moisture will gather on the bottom of the box, where it leads to mold, where the fruits and vegetables touch it.

So you keep the slider somewhere where you have great greens/fruits without too much moisture on the bottom and sides of the box.