I can make a claim without a citation, or attribute it to "some article I read awhile ago". No one can verify my original claim. Someone may attempt to dig up another citation refuting it, or find a suspect source making my claim, but these are inefficient ways of fact checking. And if I wanted to be a dick, I could claim that wasn't what I was talking about / my original source.
I can also cite my claim. In this case, 99% may accept it at face value, but 1% may fact check my citation and loudly pronounce it doesn't conclude what I said it did. The 99% then gain the benefit of an erroneous report.