This feature is used for addressing various shipping requirements of your catalog of products. Typically you would have different categories for different size of products. For example you may have a customer who orders a pallet of coffee beans and one coffee jug. You could have a default category for standard shipping, such as the coffee jug and another category for over-sized products such as the pallet of coffee beans.
This is what the customer will see and shows the carriers and services used to send your products.
Delivery / Ship Schedules
A delivery, or ship, schedule is the set of available days which a customer can request a delivery for. Ship schedules are only applicable if you've selected to enable Delivery Date Selection.
For example, if you have a group of vendors in Brooklyn that you deliver to only on a Monday, Wednesday and Friday, you can create a ship schedule (step 1 below). and attach your customer accounts to this shipping group (step 2 below).
At the bottom of the edit customer page, you'll find the option to select the ship schedule which you want to assign. You can also customize the delivery dates for that customer directly here.