Magento

As I understand it, Catalog Price Rule > Actions > Stop further rules processing relates to other Catalog Price Rules only, not Shopping Cart Price Rules. If that’s correct, then CPR needs an option Combinable with Shopping Cart Price Rule [Yes/No].

If you for instance have a heavily discounted product (using a CPR), you might not want to allow additional discounts via Shopping Cart Price Rules (e.g. using a limited time coupon for 20% off on everything), as you could otherwise actually lose money instead of making it.

This issue has been discussed earlier in this forum thread.