What is the central message of your web page? Whom are you talking to? What are the main issues of the page`s visitors? And what are the reactions you hope to effect?
The concept of your website is decisive for many questions of your project, beginning with design and pictures, menu structure, needed components, accessible coding and so on.
A taxation of your capacities and the time you can spend actualizing the website is part of the concept, too.
Many ideas are developed during the conceptual phase.
For the future development every idea they might be helpful.
Ascertaining priorities is fascilitating future decisions of the project. And it helps structuring the contents in the backend.