Since an en dash (–, half the width of one em) is not readily available on a usual keyboard while a hyphen (-, quarter the width of one em) is, the two are often confused. This is especially unacceptable in a LaTeX document since one can type two hyphens (--) to make an en dash (and --- to make an em dash).
En dashes are for juxtaposing different things, e.g.
or for ranges of values, e.g.Hyphens are for compound nouns and adjectives, e.g.