Originally Posted by HarryT
Full justification is where you insert additional space into a line so that the right margin "lines up" all the way down the page. Virtually every printed book and magazine uses full justification.
Left justification is where the left margin "lines up", but the right margin is "ragged", with no additional space being inserted.
While printed books use full justification all the eBook devices do not do a very good job with real justification. They simply insert additional space characters between the words. A sometimes they don't even to a good job of picking the places to insert the spaces resulting in a visual river running down the page. In addition the lack of support for proper hyphenation causes increased problems with full justification on the short lines used on most readers.
A good printed book actually increases the space between characters in the word and use variable width spacing to accomplish the professional look. Short lines of text typically don't do well with full justification which is why some newspapers have abandoned it.
Of the electronic formats for books we read PDF is the only format that will generally do a good job of full justification. There is a lot of improvement needed in eBook software before it becomes my preferred format. This is why left justification is useful, currently, for eBook readers and should be offered as an option.