Single purpose classes to set the font-weight of any element at any breakpoint.
Varying the font-weight of different pieces of text can help create contrast between pieces of information. It can help call attention to a piece of content, or help to make a smaller font-size a bit more readable. In Elements of Typographic Style, Robert Bringhurst suggests we keep two things in mind when playing with font-weight. Use bold weights sparingly. Font-weight should decrease as font-size increases.