Visual Explanations Images and Quantities, Evidence and Narrative. by Edward R. Tufte.
Tufte says that relevant to nearly every display of data, the smallest effective difference is the Occama's razor ("what can be done with fewer is done in vain with more") or information design... data displays must be clearm assured, reliable, sturdy. In designing information, then, the idea is to use just notable differences, visual elements that make a clear difference byt no more - contrasts that are definite, effective, and minimal.
My example of using pointers/lines to show important information on the screenshot.