Webdriver object creation basic query

WebDriver cd= new ChromeDriver(); ----1

As per this line we mean that we are accessing object of Chromedriver through reference variable of interface Webdriver.

I have gone through interface explanation in your module and i am aware of above concept.

We can also write

ChromeDriver cd= new ChromeDriver(); -----2


Please explain with some basic example whats difference between these two commands.
As class which implements interface have to implement all the methods declared in interface .


So if all methods are used by Chromedriver which are there in Webdriver , what addidtional benefit we are getting from statement 1.