Compatibility View determines how Internet Explorer identifies itself to a Web server and determines whether content is rendered ...

Compatibility View determines how Internet Explorer  identifies itself to a Web server and determines whether content is rendered in Internet Explorer 7 Standards Mode or the Standards Mode available in the latest version of Internet Explorer.
      
If you enable this policy setting, Internet Explorer will use an Internet Explorer 7 user agent string (with an additional string appended). Additionally, all standards mode Web pages will appear in Internet Explorer 7 Standards Mode. This option results in the greatest compatibility with existing Web pages, but newer content written to common Internet standards may display incorrectly. 

If you disable this policy setting, Internet Explorer will use a current user agent string . Additionally, all standards mode Web pages will appear in the Standards Mode available in the latest version of Internet Explorer. This option matches the default behavior of Internet Explorer. 

If you do not configure this policy setting, users will be able to enable and disable the Internet Explorer 7 Standards Mode.