If you sell products, getting the categories of your product right, is just as important as getting the right keywords, as it is both useful to the search engines and potential customers, making it easier to find your product either to list or to buy, you should therefore make sure that you have all your products categorized correctly. I found a classic example of this whilst I was searching the the net looking for electrical books instead of finding these books where expected on a specific website, I found gardening books, simply because that is the way the search engine indexed them.