Allows the same controls that you get with HTML to apply to cookies, so far I had been using the Web Developer toolbar to view/change cookies, however this allows for much easier editing. It also has a feature to show you when cookies are changed, which is great for debugging.
This is useful to work out either why your site is running slow, or for you to make improvements to make it faster. It has various rule sets which can be found here which define what exceptions it allows.