When you get to the level of abstraction demonstrated in the Facebook Margins example, you have so many classes for each element that you may as well go back to inline styles.
This also enables inconsistent UI in the front-end: some of my page-headers can have .mbl "Large bottom margins" and some could have .mbs "Small bottom margins".
This also enables inconsistent UI in the front-end: some of my page-headers can have .mbl "Large bottom margins" and some could have .mbs "Small bottom margins".