A short excerpt from Beautiful Evidence in which information design master Edward Tufte makes a solid case for function leading form:

The Sixth Principle for the analysis and display of data: Analytical presentations ultimately stand or fall depending on the quality, relevance, and integrity of their content. This suggests that the most effective way to improve a presentation is to get better content. It also suggests that design devices and gimmicks cannot salvage failed content.

The content principle points to priorities in analytical design work: this is a content-driven craft, to be evaluated by its success in assisting thinking about the substance. Thus the first questions in constructing analytical displays are not “How can this presentation use the color purple?” Not “How large must the logotype be?” Not “How can this presentation use the Interactive Virtual Cyberspace Protocol Display Technology?” Not decoration, not production technology. The first question is What are the content-reasoning tasks that this display is supposed to help with? Answering this question will suggest choices for content elements, design architectures, and presentation technologies.