On typographical matters, I generally seek advice from two sources:
Robert Bringhurst, The Elements of Typographical Style
James Felici, The Complete Manual of Typography
Bringhurst, who generally prefers justified lines in setting books,
has this to say about the occasions when ragged right might be
preferable:
"In justified text, there is always a trade-off between evenness of
word spacing and frequency of hyphenation. The best available
compromise will depend on the nature of the text as well as on the
specifics of the design. Good compositors like to avoid consecutive
hyphenated line-ends, but frequent hyphens are better than sloppy
spacing, and ragged setting is better yet.
Narrow measures - which prevent good justification - are commonly
used when the text is set in multiple columns. Setting ragged right
under these conditions will lighten the page and decrease its
stiffness, as well as preventing an outbreak of hyphenation.
Many unserifed faces look best when set ragged no matter what the
length of the measure. And monospaced fonts, which are common on
typewriters, always look better set ragged, in standard typewriter
style. A typewriter (or a computer-driven printer of similar
quality) that justifies its lines in imitation of typesetting is a
presumptuous machine, mimicking the outer form instead of the inner
truth of typography.
When setting ragged right from a computer, take a moment to refine
your software's understanding of what constitutes an honest rag.
Many programs are predisposed to invoke a minimum as well as a
maximum line. If permitted to do so, they will hyphenate words and
adjust spaces regardless of whether they are ragging or justifying
the text. Ragged setting under these conditions produces an orderly
ripple down the righthand side, making the text look like a neatly
pinched piecrust. This approach combines the worst features of
justification with the worst features of ragged setting, while
eliminating the principal virtues of both. Unless the measure is
excruciatingly narrow, it is usually better to set a hard rag. This
means a fixed word space, no minimum line, and no hyphenation beyond
what is inherent in the text. In a hard rag, hyphenated linebreaks
may occur in words like self-consciousness, which are hyphenated
anyway, but they can only occur with manual intervention in words
like hyphenation or pseudosophisticated, which are not."
Bruce
