I believe it could be usefull for CSS selectors[1]

The following rule will match for values of the "lang" attribute that begin with "en", including "en", "en-US", and "en-cockney":

    *[lang|="en"] { color : red }

So you may now be able to select with CSS elements with that syntax, for example matching all text-warning, text-info, text-center etc with just

    *[class|="text"] { font-weight: bold }

Correct me if I'm wrong.

I don't know if it would be practical or not. Other than that it just a matter of preference, CSS classes tends to be generally separated by dashes from my point of view, whether I prefer Camel Case or not.

[1]: http://www.w3.org/TR/CSS2/selector.html#attribute-selectors