Bokeh is the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens. This is an example of this phenomenon made with my previous Rollei, the f2.8 Planar shot wide open at f2.8. By the time you stop down a couple of stops, the lens becomes its sharpest, but Bokeh disappears. As I shoot mostly landscapes where great depth of field is desirable, most of my medium format work is shot at f11 and large format work at f32.. But sometimes as with the photo of Mr. B above, it is fun to open the lens to the widest aperture and get clear focus only in a minute spot that emerges from a blurred background (and sometimes, depending on where you focus, the foreground as well). Even when shooting digital, as long as you are manually controlling exposure, using your lens wide open works well with portraits, where you should use the eyes and nose as focus points. Fences are also interesting when shot at a tight angle wide open, such that the first pole is in sharp focus, but each pole thereafter gradually becomes more out of focus, culminating in a complete blur. Try it.
"No place is boring if you've had a good night's sleep and a pocket full of film." Robert Adams