With one bar (14psi), the tire grip is incredible. The contact surface is very large and the tires seldom, if ever, slide on loose ground. Even on the roughest terrain, the tires literally stick to the ground.
The tire is the most sensitive cushioning element on the bike. The extra cushioning and traction because of the low air pressure leads to much better control over the bike and allow distinctly higher speeds.
All this without the risk of snake-bite punctures. Dented rims become a thing of the past. Significantly lighter tires can be used in even the toughest conditions. What is more, the additional air chamber has excellent emergency running characteristics.