Selenium-WebDriver makes direct calls to the browser using each browser’s native support for automation. How these direct calls are made, and the features they support depends on the browser you are using. Information on every ‘browser driver’ is provided later in this chapter.
For those familiar with Selenium-RC, this is quite different from what you are used to.
You may, or may not, want the selenium Server, depending on how you intend to use Selenium-WebDriver. If you may be solely using the WebDriver API you do not need the Selenium-Server. If your browser and tests can all run on the same machine, and your tests only use the WebDriver API, then you do not need to run the Selenium-Server; WebDriver will run the browser directly.
There are some reasons though to use the Selenium-Server with Selenium-WebDriver.
You are using Selenium-Grid to distribute your tests over multiple machines or virtual machines (VMs).
You want to connect to a remote machine that incorporates a specific browser version that's not on your current machine.
You are not using the Java bindings (i.e. Python, C#, or Ruby) and would like to use HtmlUnit Driver.