Most stores will have a couple of products that are different in size, shape, or weight from the rest of the products, and trying to create one set of rules for all of your products can be a bit tricky. You might end up not estimating enough for some orders and estimating too much for other orders. Neither one is good for your business.

To help store owners, WooCommerce has shipping classes that allow you to group your products. With multiple groups you can create different shipping rules for each group, which will give you much more accurate shipping estimates. These shipping classes are used throughout WooCommerce. They're used in Flat Rate Shipping (which is included in WooCommerce) and some of the WooCommerce extensions like Table Rate Shipping.