Sure, no offense taken!
There are multiple benefits, but to start, you can put an article in multiple categories versus only one namespace, and categories aren't at all tied to the address of the article.
The
Type 30 nekovalkyrja service pistol is located in the stararmy: namespace. If you ever wanted to recategorize it, any references to it would be broken, or at the very least would end up linking to a redirect page.
Furthermore, there is no easy way to simply look up all stararmy related articles without manually creating a page that links to all of the relevant pages or drilling through the sitemap which is awful and bad*.
With categories, putting something in the 'Weapons' category creates a link at the bottom of the page taking you to the weapons category page which is a page that automatically adds and alphabetizes all pages that are in the weapons category. Additionally, you can put something in multiple categories: in the example above you could put it in a weapons category, a Star Army category, and a category for the year it was first introduced. Even better, you can create subcategories, so it could also be tagged as a side-arm, and a military weapon.
This leads to a system that greatly enhances the ease of navigation on the wiki and reduces maintenance by obsoleting pages like
this.
Combined with templates (if those were added as well), you can do some really powerful stuff. For an example of this in action, check out the
wikipedia article on the GURPS roleplaying system. The bars on the right and the bottom are templates which if you view the wiki code are added with only "{{RPG}}" and "{{RPG systems}}". Below that, past the "This role-playing game related article is a stub. You can help Wikipedia by expanding it." text is the category bar. You'll notice it has the categories of "Role playing Games" and "Role playing game stubs". The first of which was added with only the code "[[Category:Role-playing game systems| ]]". The stub category was added as part of a template, and I won't get into it.
Now, if you click on the roleplaying game system categories, you get taken to a big list of alphabetized articles relating to roleplaying game systems, including some sub-categories. This list is automagically updated without any human intervention as pages are placed in or removed from categories.
*This is for a variety of reasons, but ideally, you don't want to have a billion namespaces either.