"Class names tell what the stuff is" is not a "real world use case or benefit". In an HTML document, the defined vocabulary is the HTML elements and some attributes. Class names are styling hooks, with the exception of microdata.
'red-12px-right' is a stupid class name (and a strawman). A better example would be 'heading-primary', instead of a "semantic" approach like '.news h2 { }' (which could have the same styles as '.blogs h1' and '.members h3'...)
'red-12px-right' is a stupid class name (and a strawman). A better example would be 'heading-primary', instead of a "semantic" approach like '.news h2 { }' (which could have the same styles as '.blogs h1' and '.members h3'...)