The cached page feature means your website can be up even when it's not. This afternoon, nVidia's main web site was down -- it looked like one of their internal servers was offline, so the web server couldn't find some file it needed. But it was awake. I had just received a new graphics card, so I really needed to get the latest driver downloads.
two comments, already:
It’s also quite useful when you’re looking for pages long-gone, not just temporarily down.
Matt (osarusan at gmail dot com)