Paraphrasing is to explain with your own words a document made by other author. In which way you present a completely new document, usually shorter than the original one, and emphasizing more the main idea of the source. It’s different from summarizing because it explains also the supporting ideas and not only exposes the main idea, because it could be said is a preview from the source document.
I prefer more this writing tool because it helps you retain better the concepts in your mind and helps you writing a more understandable document for yourself or even for others from complicated sources.