How to apply the rule actions to a subset of products
When editing a rule, you may have the option to only apply the rule actions to a subset of products. This is shown in the "Apply the rule actions only to cart items matching the following conditions" field usually in the "Actions" tab of a rule edit screen.
This setting allows you to filter a subset of the products that the action applies to. Only the subset matched products will be used towards calculating the total number of points earned/required-to-spend (depending on whether the rule is an earning or spending rule).
If left blank, this will use any items in the cart that matches the Conditions to calculate the total points earned/required-to-spend.