The Norton recycle bin protected files contains more than just files you have deleted. It also contains extra files from software installs, internet downloads, and even from Microsoft updates. It will also store the files it deletes when you run a Windows repair using one of the utilities in Norton System Works.
Unless I'm mistaken, somewhere in the Norton configuration there is a time limit you can set for it to start deleting the files on its own. You set it for whatever you feel comfortable with and it will delete files on that day count based on the day they were imported there.
Don't use Norton any longer, but when I did I used to just delete everything in there and I never had a problem. Maybe I was lucky?