Writers who already release their works under Creative Commons licenses – an alternative to copyright, which permits forms of reuse and reworking – do so for a variety of reasons, such as encouraging extracts and fan translations.
Over the weekend, and from the Observer of all places, an example of the bizarrely common misconception that Creative Commons licenses have anything to do with copyright. It’s a grant of rights to distribute/use/create derivative works from something with certain limits, and leaves copyright well alone to the original creator. I’ve seen authors get this wrong, usually when discussing piracy (“A license to steal copyright!” etc.), and it’s really not that hard to grasp. Grant of rights. Distribution/usage under given terms. That’s all.
Creative Commons does have its own ‘CC0' tool for releasing work to the public domain, but that's very rarely used (it was only through Google that I learned it even existed; I've only ever seen their regular licenses in play). Even then I'm not sure if it affects copyright; it may simply 'copyleft' the work like the GNU GPL.