WP as a CMS: using categories for navigation

I’ve set up WP as a CMS. As a tweak, I’ve made a navigation bar at the top of the page. And in that bar, I’ve encountered a (maybe philosophical) problem:

There are three types of links.

– A ‘news’ link that is displayed as active if there are any search results or archive pages being displayed, or, if the actual blog is being viewed.

– Static page links, as in pages to e.g. About me.

– Links to categories that aren’t shown in the sidebar, which is useful to emphasize on certain categories, such as Services.

That last type of link is what I think to be a bit confusing. I’ve got the idea of using categories in the navigation from another website; however, while it feels like it’s on the tip of my tongue I can’t quite grasp the advantage of categories in navigation of pages. If I add e.g. a new service or a subservice to an existing type of service, what benefit does a post in a category Services have over adding a child page to an already existing page?

There is one that I can think of right now: You can tag a category while (apparently, correct me if I’m wrong) you can’t tag a static page. Thus, you could add a new service and simultaneously announce it in the News category. Thus, you’d have it listed in Services (which is similar to a static page) and at the same time, without having the same entry again on the News, which is dynamic and will be replaced with newer things.

So, in summary, what I’m looking for is: What other advantages do you think does having catgegories as navigational anchors/links provide?