The 737 FCTM mentions a cockpit window can be opened in flight (unpressurised of course) and an area relatively free of wind blast is available.
Operating into Pacific atolls we occasionally encountered extremely heavy rain which blotted out forward vision. Alternate airports could be between 300 to 500 miles away and no certainty the weather would be good at the alternate. It was comforting to know that when all else fails and you had no choice but to land or ditch, the option was available to open a window and by tilting your head close to the open window you had enough forward vision to get the aircraft on the deck. The problem was always blinding rain obscuring the windshield and the window open option gave you a good chance of seeing more clearly.