Although I've never seen this particular feature in cPanel, I believe it is used to control mod_deflate. Please take a look at this wiki article for more information: http://httpd.apache.org/docs/2.2/mod/mod_deflate.html
my students that have accounts on x10hosting's free-hosting server [ xo4 ] and [ xo5 ] - say they have [ Optimize Website ] on cPanel X3's main page
at that link in cPanel - it says "This feature requires Apache’s mod_deflate to function correctly"
and this post say it will NOT work --> [ http://community.x10hosting.com/thr...ince-update-to-apache-2-4.195079/#post-935483 ]