Ok Slick, one example: In Polybius' description of the Ptolemaic reforms prior to the battle of Raphia, he says that the Ptolemaic army was reorganized along ethnic lines, each nation to their own unit, and equipped with their nation's weaponry. By studying papyri, we can show this was not the case.

That's a very simple one, but I hope it's sufficient to show what I mean. Besides, I think you missed my point: we're not talking about modern sciences, we're talking about using an alternative, less accessible, often superior type of ancient source.