A popular typography technique in the print world is to justify text. The following paragraph is an example of this style:
Hac dictumst elit. Non turpis, nec sit habitasse massa sed sagittis et, purus lundium porta auctor augue in platea tincidunt non urna, eu elit magna aliquam proin ut, vel, odio et vel cum mid integer magna velit pellentesque augue ac! Lundium lundium vut ut facilisis, proin placerat ut, ultricies ut, ac habitasse. Purus sed. Massa, est, dapibus? Dis ac sed, sed ridiculus dolor nunc. Purus odio, duis? Odio non dignissim? Magna quis adipiscing tincidunt et ultrices montes nascetur, in ultricies augue?
What many clients do not realize, however, is that formatting a page with justified text is a bad practice on the web. The following are a few reasons why justified text should be avoided on the web.
Monitor Refresh Rate
Computer monitors actually flicker at a very rapid rate, and the number of times per second that this occurs on a monitor is called the "refresh rate". As a result, we are actually reading moving text as we move our eyes, and this causes eye strain. This makes reading text on a monitor much harder on the eyes than reading from a printed page.
Lack of Control
In traditional print media, the typographer has control to fine tune the text on the page and ensure that it is presented exactly as intended. Due to variations in web browsers and screen resolutions, this is nearly impossible to do on the web. It is very likely that a person browsing your site using Internet Explorer will see text rendered differently than a person browsing with Firefox.
Rivers of White
Variations in rendering among different web browsers can create "Rivers of White" which are gaps in typesetting. These rivers can distract the user and make the text much more difficult to read. See this Wikipedia article for more information.
Dyslexic Users
Is is believed that between 5 and 10 percent of the population are affected by dyslexia. The points listed above can cause serious problems for users affected by dyslexia. Rivers of white, for example, can sometimes form more distinct patterns than the words themselves.
Screen Magnifiers
Visually impaired users often user screen magnifiers to enlarge the text that they are reading on the web. Large uneven spaces and rivers of white get magnified in the process, and this makes it difficult for the reader to follow the words.