I'm not sure if this reply is directly on the point you want to ask about: "categorizing Hubs" could refer to the subject choices you are offered when you create the Hub, but also--though this isn't the terminology Hubpages uses--the "Groups" you can construct for yourself to organize your Hubs.
As to the first meaning, I haven't found the categorization to make that much difference. I have, for example Hubs on global warming, and due to the multi-disciplinary nature of that topic they could be categorized under 'physics,' 'environment' or 'politics and society'--probably under a few others as well. I haven't been consistent in picking one category and sticking to it--but it seems not to affect the Hub traffic to any noticeable extent. So I just pick the category that seems most logical in the moment that I'm creating the Hub, and don't worry about it thereafter.
On the other hand, I do use the "Groups" feature quite a bit. It has several advantages.
First, it lets readers navigate directly to a succeeding or preceding Hub in a series with one click. That's a convenience for them, and possibly an increase in traffic for you.
Second, it lets me easily organize and compare related Hubs. And you can re-Group them easily as better ways of organizing occur to you--it is very flexible.
Third--and related to the second point--it can be very helpful in finding relevant Hub statistics when you want to check on something specific. For example, suppose I've back-linked to a Hub of mine from a discussion on an external Blog site. Later that day, I want to check to see if this link has generated any page views. With 51 Hubs as of this writing, it's easy to overlook the one you want to check on as you wade through the list. But select the Group to which that Hub belongs, and it becomes easy to pick it out of a half-dozen or so Hubs rather than 50.
Hope that helps!