With the help of "Root" directory you can access your system files modify them and do lot of changes and modifications which otherwise can brick your phone so do it on your own risk.

if you are rooted it means you have the full power on your phone. it is dangerous if you don't really know what you are doing because third party app can download malware and destroy your phone. but otherwise it is really powerful, just take a look at GravityBox or the XPosed framework. please note that Pokemon go or Snapchat won't work if you are rooted