DMCA take down notices are meant to protect intellectual property. However, large companies often take advantage of them and send millions of these take down notices per month through automated systems. Many of these are not valid. These systems hurt people who create legitimate content as they are not checked for errors. When site owners receive requests, they feel pressured to remove content or links.
For example, HBO has asked Google to remove links to HBO.com (http://tinyurl.com/b735pyn), Microsoft has asked them to remove links to Wikipedia, BBC, and the US Government (http://tinyurl.com/8l7bxgm), and Warner Bros has even admitted to removing content it doesn't own the copyright to (http://tinyurl.com/d7ys42w).
These requests must be error-checked to protect legitimate content.