answer:Really none. By developers, cookies are considered public data. No decent security would rely on them as they are stored on your computer. Anything important will be stored with the site instead and at most confirmed with the cookie. They’re basically a handy way to store non-critical information without needing an account. A lot of people clear their cookies every time they exit a browser, so they should never really give or take much information or functionality on their own. There may be some unintended consequences of messing with them, but again it should be limited. Ethically, it’s the equivalent of telling telemarketer you don’t remember talking to them before. Not really the type of thing you’ll burn for ;) Editing to add: you might be a little careful if you find something that’s actually of value that you can get free by editing cookies. The people behind it would be idiots, but some of the things that have been considered “hacking” in a legal sense are even less technically involved, and further against “best practices”.