Manuscript Preparation, Copyediting, and Proofreading
Q. In terms of full or ragged-edge justification of documents, which one is preferred for which type of document: business letter, research paper, sales and marketing materials?
A. Full justification is most often appropriate for typeset materials that have been professionally designed. All other materials should be ragged. In many cases you can judge for yourself: if full justification causes some lines to stretch out and others to squish together even when automatic hyphenation is turned on, it’s better to go ragged.