Why would I want to put information on my web page that is not visible to the typical viewer?
You need certain codes like binary code or doctype html code to program a webpage to do and say certain things. But this code must be invisible because to the most ordinary person, they would think the website isn't working because of all the code on the screen. Thats why you have it invisible so no one can see it.
Metadata is needed to encript code to display cetain aspects of a webpage. For example the background color, the author and viewpoint.