There are a few advantages of using WebDriver over the Selenium Server:  WebDriver is a more powerful tool for controlling a web browser because it can directly interact with the browser, whereas Selenium Server can only control a browser through "injecting" JavaScript commands.  WebDriver is faster than Selenium Server because it speaks directly to the browser and doesn't need to start up a new instance of the browser.  WebDriver is more reliable than Selenium Server because it can detect the state of the browser and respond appropriately.  WebDriver is more flexible than Selenium Server because it supports a wider range of programming languages, browsers, and operating systems.  WebDriver is easier to use than Selenium Server because it has a more intuitive API and requires less setup.  WebDriver is more lightweight than Selenium Server because it does not require a separate server process to be started. This can be especially beneficial in environments where resources are limited.