"Chart junk" -- the noisy visual elements that attract criticism in design circles -- can help make a data visualization more memorable. And the chart types we learned about in school (bar graphs, pie charts, etc.) are not the easiest to recall.
Tension is good. It makes the reader turn the pages. However, constant high tension soon gets dull. The readers can't sustain continuous scared excitement, and after a while, instead of roused, they become bored.