As a merchant, you should know the pros and cons of automated categorization. Automated categorization has both benefits and drawbacks.  Let's talk about the benefits first. Automated categorization ensures that you do not need to assign your product categories one by one as per the Google Taxonomy list. It means that you can save your time from going through the list of 6000 product categories. It will help you start advertising quicker.  Now, let's face the drawback.  Though automated categorization may seem to be a time-saver for you, it is like a gamble to leave the complete categorization part merely on algorithms. It should be your priority to make sure that your products are assigned with the proper categories and never otherwise.  The automated assignment of the category relies on the product title, brand, GTIN, description, etc. That's why it's likely for the algorithm to make a mistake in determining the right category.  An issue that comes as a result of the wrong allocation of the category is that incorrect assignment often leads to tax miscalculation, especially for those merchants who sell their products in the US market.  If you want to get rid of all these drawbacks, it's best to optimize your product feed by using the category mapping feature of any popular third-party plugins like CTX Feed.  Also, if you want to have greater control over your campaign targeting, it would be wise for you to categorize your products precisely.