The primary purpose of Order Categories is organization. If you ever find yourself saying, “I wish I could just see a specific kind of order on my Orders page,” then Order Categories are for you.
Usually, Orders are put into Categories with automation Rules that identify parts of the Order and sort them into Categories, which can then be easily filtered for on the Orders page.
For example, you can create an Order Category for your First Class orders, or Pre-orders, or any other attribute that you can think of.
Note: Each Order can only be in one Category at a time.