Categories is a concept that helps users to find relevant information and navigate on the site. Preferably, each page should be assigned one or more categories. The original author of a page can do this, but also others can step in and help later. Thus, the founder of the site will from time to time check whether categories are assigned. You will get an idea about the usefulness of categories by inspecting the Categories page. It provides a structured way to access any page that has been categorised.