We are interested in the content -- not the necessarily the exact language used by the author.
Sometimes, using the author's exact language is the most effective way to convey his or message. In this case, you may want to quote. Otherwise...
Paraphrasing demonstrates a command of the subject matter or concept. You are able to take someone else's idea and explain it in your own words, which conveys authority.
Paraphrasing may clarify the content for your reader. Furthermore, when you paraphrase, you make connections between another author's ideas and your original ideas. Paraphrasing allows you to integrate someone else's content into your own work without interrupting the flow.
