Justification is typically achieved by adding or removing space between words, and less commonly by adjusting the space between letters and the width of the letters themselves.
(Typically, the last line of a justified paragraph is set flush left.)
Because it introduces uneven spacing and removes visual anchors created by a ragged right edge, justification is often less readable than flush left alignment.
The main attraction of justification is that it creates a visually pleasing page, especially if the text is arranged in more than one column. Newspapers and magazines often use justification.