After opening hundreds of windows and you want to desperately do something with your desktop, you have to go on minimizing all the windows. This is where the Show Desktop is used. For those who have not seen it, it is there in the quick launch section of the Task Bar.
And for the more unlucky guys who have not enabled the quick launch, a google search would be more than enough to know more.
And for the lucky guys like me, who occassionally find it interesting to accidently delete files ;), here is the Show Desktop file
Filename : Show Desktop.scf