Fully open, louvre blades are close to horizontal. This means they provide very little resistance to the air entering through the window opening. In effect, you get twice as much ventilation as you would though a same sized sliding window or double hung window.
The benefits of Louvre Windows over other window types don't end with ventilation. When open, they don;t get in the way of passing traffic. They can be left open in gentle rain. And the inside and the outside surfaces can be cleaned from inside the building (handy in multi storey buildings.