Tilt 'n Turn windows are predominately used to overcome the need to easily clean upper floor windows from inside. The 'tilt' position (right) refers to the ventilation position. 

The 'turn' position (left) refers to the cleaning position.

or if there is a height issue to overcome. The two lower frames on the angled facet of the conservatory to the left have the tilt 'n turn function. The normal 'hopper' ventilation function is not very practical in this situation as they are above the height of the door and more difficult to reach.