man.hyphenate — Enable hyphenation?
If non-zero, hyphenation is enabled.
The default value for this parameter is zero because groff is
not particularly smart about how it does hyphenation; it can end up
hyphenating a lot of things that you don't want hyphenated. To
mitigate that, the default behavior of the stylesheets is to suppress
hyphenation of computer inlines, filenames, and URLs. (You can
override the default behavior by setting non-zero values for the
man.hyphenate.computer.inlines parameters.) But
the best way is still to just globally disable hyphenation, as the
stylesheets do by default.
The only good reason to enabled hyphenation is if you have also enabled justification (which is disabled by default). The reason is that justified text can look very bad unless you also hyphenate it; to quote the “Hypenation” node from the groff info page:
Since the odds are not great for finding a set of words, for every output line, which fit nicely on a line without inserting excessive amounts of space between words, 'gtroff' hyphenates words so that it can justify lines without inserting too much space between words.