Seeing is understanding
"It is often difficult to understand or communicate information from complex or large datasets generated by computational simulations, experiments, or observational instruments. Scientific visualization is the computational science discipline that provides the techniques, algorithms, and software tools needed to extract and display important information from numerical data."
-Berkeley Labs/NERSC Report
Visualization
As the ancient Chinese proverb states: "A picture tells a thousand words."
Analysis
Patterns emerge from diagrams and charts that may not be identifiable from the raw data alone - even when using the most sophisticated statistical software. Often, however, a 2D or 3D representation of numerical data can assist an expert's own intuitive judgement.
Communication
Graphics help to convey ideas and concepts to others. That is as true for a data analyst presenting a report to their clients as it is for an architect helping people to visualize the design of a new building.