To know why Adsense is essential for your content sites is to know first how this works.
The concept is really simple, if you think about it. The publisher or the webmaster inserts a java script into a certain website. Each time the page is accessed, the java script will pull advertisements from the Adsense program.
The ads that are targeted should therefore be related to the content that is contained on the web page serving the ad. If a visitor clicks on an advertisement, the webmaster serving the ad earns a portion of the money that the advertiser is paying the search engine for the click.
The search engine is the one handling all the tracking and payments, providing an easy way for webmasters to display content-sensitive and targeted ads without having the hassle to solicit advertisers, collect funds, monitor the clicks and statistics which could be a time-consuming task in itself.
