This template is used to easily make the em dash (—) character, not supported by most keyboards.
The — is used to indicate an abrupt change of thought or an interruption in the linear flow of a sentence. It is frequently used in lists to separate a short 'prefix' from additional information, or to indicate an open range of dates. The em dash is twice as wide as a hyphen/minus sign.
For further information, see also: Wikipedia:Dash.