All given answers here seems to be only for English.
I just want to add another language: German.
German has a lot of long words (much longer as English words). If you want to typeset a German text on paper with justification you can't do it without hyphenations. LaTeX does a very good job with automatic hyphenations for the German language. It also knows the rule that in German there are only a maximum of 3 rows above each other with hyphenations are allowed.
Hyphenation is only bad if it can change the meaning of the hyphenated word, for example the German verb "beinhalten" should only hyphenated as "be-inhalten" (contain, containing) and not as "bein-halten" (could be read as "Bein halten" (leg hold)).