Humans are highly visual. Long before we can walk or talk, our eye is expertly registering, groupings, colors, spatial relationships, and other information-rich patterns and qualities. Yet we rarely make full use of the incredible power of visual communication.
Paradoxically, a great place to see this is in all-text documents. That’s because readability depends heavily on structure and navigation, and visual cues can convey these readily.
Good visual cues kick-start the process of comprehension and reward the reader’s attention. Poor visual cues do the opposite. Even an absence of good visual cues hurts readability, forcing the reader to spend more energy getting oriented and making them less likely to want to keep reading.
What’s an example of what we mean by good visual cues? This page, for one.