Why WebDriver driver = new ChromeDriver() ?

Below is WebDriver Interface & Respective class implementation architecture.

ChromeDriver driver = new ChromeDriver(); // Lot of methods from parent calss RemoteWebDriver

vs

WebDriver driver = new ChromeDriver(); // we can access only few methods from WebDriver Interface & SerchContext Interface

Ex: Advantage of interface

Public List getList(){
       return new ArrayList<String>()
}

We can return any implemented class for any method which has return type as interface