Hyphenation makes the text density (the greyness, or the distribution of "ink") more uniform on the page, i.e., the spacing between words will be more consistent. It is common practice to use hyphenation if the text is left and right justified, but not use hyphenation if the text is centered or is not justified on one side. You can disable hyphenation by adding \hyphenpenalty=100000 just before \begin{document}