Some people like fully justified text. I guess it brings another layer of perceived order to an otherwise chaotic universe. If you choose to implement it on a web page, be warned that legibility suffers due to the crude justification algorithms implemented in browsers.
But even with sophisticated page layout software, justified text blocks often suffer from poor spacing and excessive hyphenation and require manual refinement. This level of control is not even a remote possibility on Web pages. The most recent browser versions (and CSS) support justified text, but it is achieved by crude adjustments to word spacing. Fine adjustments are not possible on low-resolution computer displays and are impractical to implement in today’s Web browsers. Also, Web browsers are unlikely to offer automatic hyphenation any time soon, another "must" for properly justified text. For the foreseeable future, the legibility of your Web documents will suffer if you set your text in justified format.