I have a personal, hosted forum here for my game. I had already designated thread tags to be used for certain types of threads. With the categories, I can do away with that. I have threads for each PC that covers "Characterization, Advancement and Goals." These threads are there to provide an outlet for the players to communicate PC quirks, ways that they want to advance (non-mechanicall) and what goals they have set. Now I have a CAG category.
I also have a Scheduling category, an RP category, a Logs category and a pure Metagame category. These will work well for my small group.
In the larger context of EN World, being able to sort based on categories within a forum could be very helpful. Ceramic DM/Iron DM are significantly different than advice on a problem Player. Alsih2o's History in Your Game might be similar or complementary to creating a homebrew campaign, but it is different from asking about which minis and battlemat type products will suit your gaming environment best. But all of these definitely still belong in the General Discussion forum. So I can see some value to the categories. Especially for the folks looking to address a current need.
For those of us that try to browse every thread to snarf anything useful from it, then the categories might not be as valuable, right now. But you never know when you will want to use them for a search parameter, or a sort mechanism.
But Barsoomcore does bring up a good point about defining each category. They need to be well enough described that most people will agree on their application. Though adding in a sticky thread or something with generally accepted definitions would be helpful.