Doesn't grab files the page uses (like JavaScript and image files) from the browser's cache. Loads them from the server instead.
The "hard refresh" = <Ctrl>+<F5> forces a download of all page components including scripts, etc., from the server, rather than refreshing some or all of the page from the hard drive cache (which could be the case foor a simple <F5>, depending on your browser settings). Damn that guy is fast