The classic example is the use of dot-headed figures to convey quantities; this clutters up the chart without adding any information, and is often used to convey an impression that turns out to be false when you look behind the data. So my immediate reaction whenever I see a publication with a lot of chartjunk is to assume that the author is trying to put something over on us.

Graphs and charts embellished with "chartjunk" may help rather than hurt people's understanding of data, a study at two U.S. universities indicates.

The interior decoration of graphics generates a lot of ink that does not tell the viewer anything new. The purpose of decoration varies — to make the graphic appear more scientific and precise, to enliven the display, to give the designer an opportunity to exercise artistic skills. Regardless of its cause, it is all non-data-ink or redundant data-ink, and it is often chartjunk.