GQ: Why would I want to put information on my web page that is not visible to the typical viewer?

It's important to put information that is not visible to the typical viewer so people who like to look through the coding of the webpage know who made it, what's it about, and how to categorize it.

Importance of Metadata

Metadata is very important to all html pages because "text crawlers" would like to know about certain types of data that is not visible to the typical user.
Data such as description of the webpage, author of the webpage, and what character set is contains.