Won't hurt anything. Most of the cookies just track what sites you've been on, and any preferences you've had on those sites with which you have interactions. The only harm you may have is, hassles for yourself.
If you purge the cookies, then you'll notice that, on some websites you were in the habit of visiting, some things you had set as preferences, won't be remembered, and you'll have to set those preferences again. No problem: just do it.
(Of course, a very few mean-spirited websites I've run into give you a real hassle, where if they find their cookies gone, they make it hard to set them up again. It takes an extra effort to deal with these, but it can be done.)
While "traditional" cookies are little tiny text files on your computer, a new technology has arisen called "flash cookies". The only way you can display and control these is to visit the Adobe website: http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html