Used for: splitting products with a list of sizes into a separate product for each size.
This rule does the exact opposite of the "group products" rule. In this case you select a field of a product that contains a list (e.g. a list of available sizes) and create separate products for each element in that list. This way, a product with a list of 5 sizes will be transformed into 5 products that are exactly the same except on the field "size".
As you can see below, the rule is quite easy to set up. Just make sure that the "size" field contains a list of available sizes, otherwise it will not work.