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

A character set is needed for the page to know what language the website is. A descriptions and keywords are needed for websites like google to know what the web page is about without reading it.This makes searching for stuff a lot easier for the browser. Authors are needed in order for people to know who made the .And the viewport is needed in order to fit the page if the user is on a bigger or smaller device like a phone or tablet. In other words you should do it for smart people who care about the website.