It does … nothing.
It used to do something.
At one point, when you did hugo new page.md, we used metaDataFormat to decide what format we would use for the front matter of the new page.
But then, at some point, I rewrote the rather complex page parsing logic – and removed this particular feature as part of that simplication …
We now treat the archetype templates as template files and do nothing further magic mumbo jumbo with them.