Since a freelancer usually (or from what I understand) takes on all aspects of their work, they don't really get hired for permanent positions and thus work off individual projects. A client hires the designer based off a portfolio and if the price/style/etc is a match, the project moves forward.
At least this is what my understanding is. If a freelancer isn't interested in being hired for permanent work, do they need a resumé to prove their skills when a portfolio is (in my opinion) has a much greater impact on what a designer can do?