This isn't really any type of spam or optimization method, just a cool way to manipulate the printer on webpages. This technique is good if you are designing a page that is a bitch to print. Ie. half the important information is cut off of the side of the document and you just print out a lot of buttons from a navigation bar.
If you would like to see this in action (if you haven't already) click on the following link and then click the print button when the page loads.
The way that this function works is to print a designated document when the print button is pressed or the print command is executed. There is a small line of code that controls this and looks like:
<link rel=alternate media=print href="test.doc">
This line of coding is to go between your <head> and </head> tags. In this line of coding the document that would be printed is test.doc (in green).
Again, this is mainly just used to create printer friendly pages for your website and is more of a design issue than a search engine issue. A lot of the time when you are printing a page from the net, the end of each line is cut off, meaning you have to decipher the final result. I myself find this very annoying, and therefore have put this up on my page, in the hope that more webmasters will think of their users.