[bookcasey]

The @extend directive, especially with placeholders, is very powerful and allows you to not repeat yourself in compiled CSS as well.

[abredow]

This is the key that I missed when I first read the article. Mixins will always be repeated when compiled. Placeholders result in combined selectors so the styles aren't repeated in the compiled CSS.

In many ways, it seems like placeholders would almost always be preferred to mixins. Though, I'm sure there are exceptions.