While that is certainly true, and you need to ensure that the changed requirement is consistent with the source (or the source needs to be changed), you also need to know what might have to change downstream to satisfy the update. Traceability cannot give all the answers as it cannot tell you that changes need to be made to downstream elements that were previously unrelated, nor can it say that new downstream elements need to be created to satisfy the updated requirement. But it certainly helps, as generally it is only linked elements that are affected.