It's not enough to simply state that a new website or online system is needed. The real question is how it should work, what steps make up the user journey, what data it handles, who it communicates with, and what result we expect from it.
During the project planning process, we organize requirements, prioritize features, and produce a brief or specification that makes implementation far more accurately estimable and manageable.
This phase can include mapping user flows, a sitemap, the system structure and the implementation logic.