Shutdown function ?!

Hello,
I’d like to know what is the shutdown function and where can I see if it works or not?
I’m thinking to buy the autoblogger plugin and they say are using the shutdown function for a pseudo-cron, to extract and publish feeds from other sources. Previously they used the wp_footer function which I know it was supposed to be in the footer and looks like this: wp_footer()
I really want to know where is the shutdown function located, what does it look like (what I’m looking for) etc.
So, please, help a noob! I’m trying to find out if it will work with my wordpress installation.
Thank you!