"Researchers Pradeep Sopory and James P. Dillard (2002) conducted a meta-analytic review of the empirical research on metaphor and persuasion. They concluded that messages containing metaphors produce somewhat greater attitude change than do communications without metaphors."Source: The Dynamics of Persuasion by Richard M. Perloff
A while ago I wrote an article at Vegan Soapbox. I felt that the piece was persuasive and compelling, but now I know why. Here is a bit from that piece:
My friend, showing me the cut he received on his face, said he thought they wanted his leather jacket. As he told me this, I thought about how the stitching on his leather jacket resembled the stitches on his face. Skin is skin.