In addition to allowing a writer to gain additional information about a topic, the correct use of outside sources also lends credibility to any essay. Statistics, quotes, surveys, and other forms of research can help a writer establish her point and ultimately influence the reader to agree with her.
If a writer uses credible sources and incorporates them well into the essay, the writing becomes better and more credible. Additionally, the greater the amount and variety of sources used in an essay, the more persuasive the writing can be.