Benefits of using <meta http-equiv="Expires"

Is there any benefit in using this in Google?

[sandpetra]

I see a very high profile site using <meta http-equiv="Expires" and a date that is 6 years ago...

Why on earth would they be using this?

What's the clear definition of use of this meta tag? Do you think it has any seo benefits at all?

[plasma]

14.21 Expires [209.85.129.104]