Too much material overwhelms students. Presenting too much material at one time takes away time for making connections. Students need to learn the relationships between concepts, not just the definitions of the concepts.
Organization is important.
When connections are seen, discussion is enhanced. When discussion is enhanced, students are thinking critically and learning. Mapping, diagraming, and graphics helps the teacher prepare the key ideas and helps the student learn. Using diagraming allows the teacher to teach in an organized manner but without notes and to connect with the students. We can condense material, yet still cover it well.