It tries to "teach" people how to change the template by inserting in the file header something like:
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
This might sound like a great idea in practice but it's broken since most people won't change it. So it just becomes line-noise that will get published, committed to VCS, etc.
A good UI would display that message differently, like a floating non-modal dialog, or some notification in the New File Wizard, but it shouldn't produce actual text that is part of the source code file.
Google seems to say about the same: there are 321.000 instances of files indexed by the search engine containing that header. And this is only on the public web, I bet there are many more closed-source code repositories filled with these lines...
