The example at left is shaded with the point, at right, with the side. The difference doesn't show up clearly in the scan, but you can see that the side shading has a grainier, softer look and covers a large area quickly (a chisel-point pencil will also give this effect). Using a sharp point to shade allows you more control, you can do much finer work, and get a greater range of tone out of the pencil.
Experiment with both to see how they look on your paper. Try shading with hard and soft pencils, too.
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