The material becomes waterproof, not what the material covers
It seems that only a few posters have worked it out. The fabric itself becomes waterproof and will not absorb moisture, but that doesn't mean that water can't go through the fabric.
Think of it like a plastic bag. you can wrap it around your hand and put it in water to keep your hand dry. Take it out and the plastic bag itself can simply be shaken dry. Now put hole in the plastic bag (like the hundreds of holes in woven fabric) and repeat. Your hand will now get wet, but the plastic bag can still be shaken dry.
So, for example, motorcycle gear treated with this won't help to keep you any drier as such, but it will prevent the gear itself from getting wet and heavy and taking ages to dry out. Leather jackets treated with this would be brilliant as they weigh heaps once they start to get water logged.