The tilted position is a burglar proof partial opening to ventilate the building without any danger of any person being able to enter through the window or opening it from outside.
A normal open window often causes a draft due to the direct path of the outside wind into the room. With a tilted window the outside air is channelled through the sides of the window, while hot air escapes through the top. You can leave the windows tilted open even during the rains (tilted approximately 150mm / 6 inches inwards).
In the turning position the window opens fully. In this position the glass can be cleaned on both sides from the inside of the building without dangerous stretching or climbing. A quarter-turn of the handle opens the window fully; another quarter turn will tilt the window.