Chrome: Mostly, your browser's cache is a handy feature. When it fails, though, it can make sites difficult to view, and it's also a nuisance if you're building a site and having trouble using the latest version. Cache Killer prevents Chrome from loading sites from its cache.
Cache Killer forces sites to load directly, and it can be enabled or disabled at the push of a button. That can be useful both for sites that don't load properly, and when you're in developer mode and want to be sure you're loading the current version.