Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
The task of planning websites has fallen on the shoulders of project managers, graphic designers, software developers, requirements analysts, web strategists, user experience experts, and information architects, to name a few. All these roles have their own perspectives of how a site should look and come together. Their individual experiences and skills associated with planning sites influence what is included in the site, how it is built, and how it is maintained. Their planning processes will emphasize their strengths, and typically, there isn't anything wrong with that.
Unless the individuals filling these roles have some insight into what Drupal has to offer and how it gets the job done, the site plan could miss some features that could make the site even better than originally thought. It could also set expectations that Drupal does not support at the moment. With some insight into Drupal and how it works, any of the people in these roles can plan a Drupal site.