Yes. Cookies are used to track your username / password and to identify the posts you've read during your current session. If your browser does not accept cookies, some CR4 functions won't work properly.
A lot of people are paranoid about cookies (and not without reason), but the simple fact is that this is how we know it's you from one click to the next.
If you don't want to use cookies, you don't have to. You can still post anonymously, but you will not be able to use all of the advanced features of CR4 (story tracking, story rating, user preferences, etc).
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Off to take on other challenges. Good luck everybody! See you around the Interwebs.