When I first seen the 'labs' button and 'Fetch as Googlebot' in Webmaster tools, I thought to myself what good is this? I can render pages in SERPs if I need to see if they're working or not - or can I?
By entering the page you want to check and clicking 'Fetch', if your page is available on the net Google will return a green tick and 'success'.
But that's not all - there may be something hidden.
By clicking on the 'success', you get a full blown view of exactly what the Googlebot sees when he visits your page.
Not very interesting if there's nothing to hide, but if something somehow got into your code, which you didn't intentionally put there, well, it could just save you, not only a headache, but also a little time in Google jail.