Rooting is the process of unlocking the developer features of smartphone.it can be easily done on Android phones and it is called jail breaking in IPhone.
You can access the developer options of your phone
You can install some application that use screenshot,location based services..
You can modify the default settings
You can delete unwanted pre installed applications
You can change the version of operating system
Once modified or deleted cannot be regained
You cannot claim warranty from your provider
Some default application may not work
You cannot reverse the rooting process
Even though there are more benefits in rooting only person who have knowledge can access the full features. And it full of user risk once it is rooted.