Yesterday I watched Grand Designs on TV where a couple restored an old 1600-century house. They found that at least one window was shut with bricks and concrete (or the equivalent used at that time), but when they opened it up the whole room changed and the light and the view the window provided was beautiful.
The reason for shutting the window, as Kevin McCloud told, was that long ago there was a window-tax (!!) in England, hence a lot of windows where shut this way.
You get what you measure.