I use it to set img floats. To make it work
- be sure to define at least one inline element class (when you defined your image float classes), for examle Emphasize=span.emph
- add a "cache-buster" to the end of the path of you css file: /sites/all/themes/mytheme/css/style.css?v1 (the "chache-buster" is the "?v1" at the end of the path. More info: http://chipcullen.com/how-to-apply-classes-ckeditor-4-in-drupal-7/)