Commented Bringhurst thus:
Use spaced en dashes – rather than close-set em dashes or spaced hyphens – to set off phrases.
[…] The em dash is the nineteenth-century standard, still prescribed in many editorial style books, but the em dash is too long for use with the best text faces. Like the oversized space between sentences, it belongs to the padded and corseted aesthetic of Victorian typography.
Used as a phrase marker – thus – the en dash is set with a normal word space either side.
(The Elements of Typographic Style, 2004, § 5.2.1)
But [space][endash][space] is longer than just [emdash]. How is the proposed solution any better?
It depends on the font whether an em dash is longer or shorter than an en dash surrounded by spaces. But Bringhurst’s comment is more about aesthetics. I also find the en dash with spaces visually more pleasing and more logical to set parenthetical sentences apart, rather than the em dash without spaces. The latter invites me to join sentences.
But it’s all a matter of personal tastes of course! :)
