Difference between jcr:lastModified and cq:lastModified in AEM

What is a need of having two different dates jcr:lastModified and cq:lastModified in AEM and when which one is used ?

cq:lastModified is present at jcr:content node level, means it is available on all those nodes whose jcr:primaryType is cq:pageContent. Where as at all other nodes types jcr:lastModified is used. In general we can say that if any content is getting modified through aem functionality it will refer and update cq:lastModified and everything else that is using JCR core functionality will refer and update jcr:lastModified. Both properties can’t be present on the same node.

Note:

jcr:content( cq:pageContent ) is a structured node and has a sling:resourceType property which points or refers to the component that contains the sling script which will be used for rendering the content.