If you really need to clip off the bottom of your bar graph for clarity, jagged lines do a wonderful job of explaining that instantly. I don't see the point of a bar graph that doesn't start at 0 or indicate an omitted range, except to deceive.
The following paper on lucidity in scientific communication has been a big influence on my thoughts. Briefly, the author stresses that you should aim for lucid pattern repetition over gratuitious variation, i.e. the repetition of the same idea communicated in similar ways, over variety for the sake of appearing to be superficially interesting.
http://www.atm.damtp.cam.ac.uk/mcintyre/papers/LHCE/lucidity...
How about if you're trying to show in detail a small change in a large number? If the scale started at zero, all bars would look equal.