Then you would have duplicates for almost every product. Is this really the only way of doing things? When someone was to look at all products, they'd see several of the same product (especially if that product was in more than two categories).
What was meant by this was that you would add the product to the database two times. Once for the Carhart category, once for the Wrangler Catagory. In other words, duplicate entries for everything except the category. 


