I would guess that a verbal one-on-one exam would show the professor who understands the material vs who doesn't, but also who actually understands it vs who just used rote memorization.

The latter comparison might end up being a distinction without a difference, as far as grading goes. But, were I the professor, I'd be interested to see how many of my students are understanding the material on a holistic level. This is my bias, though, because I'm way more interested in knowing why something occurred (and its relationship to other events) vs that it occurred on [insert date] and involved [insert individuals].