It would decouple your structure(html) from your display(css). The semantic class applied to your html could remain unchanged while you are changing the style.

It would decouple your structure(html) from your display(css). The semantic class applied to your html could remain unchanged while you are changing the style. For example, you could switch from using a css library like tachyon, to swapping it out with a custom css without touching your html/templates. You're right though, it is an extra layer of abstraction that might not be needed.