Mark Otto talks briefly about their decision to use prefixed classes with Bootstrap.

"Prefixed classes guide developers towards a simpler and more maintainable direction for building an extensive CSS design system."

He goes on to say…

"There’s no bleeding of styles or behavior from one component to another here because we treat components in a “successful state” as an idea across the design system. That is to say, we have a shared idea of what “success” looks for buttons and alerts, but the execution is scoped entirely to each independent component. No questions of where common styles are used and no concern of unintended effects, making each component more durable and flexible."

If you were wondering what an example implementation of SMACSS might look like? Bootstrap is a perfect example.