Nodejs streams vs callbacks

I read this article: http://elegantcode.com/2011/04/06/taking-baby-steps-with-node-js-pumping-data-between-streams/ and with minor problems understand the flows.

Quote:

"Suppose we want to develop a simple web application
that reads a particular file from disk and send it to the browser.
The following code shows a very simple and naïve implementation
in order to make this happen."

So, an example code looks like this:

var readStream = fileSystem.createReadStream(filePath);
readStream.on('data', function(data) {
    response.write(data);
});

readStream.on('end', function() {
    response.end();        
});

Why could we use this above when we could just do:

fs.readFile(filePath, function(err, data){
  response.write(data);
  response.end();
});

When or why use streams?