The importance of categories cannot be overstated. They provide order to the wiki, ensuring that pages have some sort of relation to each other. This relationship can be exploited by both human and robotic users to not only make finding articles a lot easier, but to also simplify wiki maintenance.
When you create an article you must put it into at least one valid category. You may temporarily post an article long enough to investigate the category tree to find an appropriate category. But no article should go longer than an hour without a valid category.
Note here the importance of the word valid. You may not add any category just to satisfy this rule. It must be one that makes sense and is a good faith effort at proper categorisation.