what is the purpose of status attribute in DNG
One answer
The status artifact attribute comes with most project templates with DNG out of the box I think. Depending on which template you use, it's a string or enumeration data attribute. And it's not a system (mandatory) attribute, hence you can remove it. So you can use the status attribute for whatever you like or need. I am not aware of a state artifact attribute with the DNG templates, but the same would apply.
And the status artifact attribute is not tied in with a review; an artifact can be in none or multiple reviews at the same time, so it even would be tricky to have a hard relation between the status and a review. If you want to reflect the status of an artifact with a review, you have to maintain that yourself manually. And probably use a custom status attribute just for the review part with a workflow defined for it.