Sometimes "looking at the thing itself" is too costly or too difficult. How can the proverbial "bright sixteen-year-old" sitting in a high school classroom figure out the truth about, say, the number of protons in an atom of gold, without having to accept the authority of his textbooks and instructors? If there were a bunch of well-funded nutcases dedicated to arguing that gold atoms have seventy-eight protons instead of seventy-nine, the only way you can really judge who's correct is to judge the relative credibility of the people presenting the evidence. After all, one side's evidence could be completely fraudulent and you'd have no way of knowing that.

Far too often, reference classes and meta-level discussions are all we have.