I read this in Quora :
Note: You should make sure if selenium-standalone-server.jar is needed in your case. If all you need is to run a WebDriver test in local machine please add java-client.jar. Its lightweight. Just for extra information, selenium-standalone-server.jar is a bundled jar that contains both API and selenium server. Selenium server is needed to run older Selenium RC tests or to run WebDriver tests in remote machines through Selenium Grid.
Assume that i am not using selenium server standalone jar file. So to run tests in local do i need to use just java-client jars or do i need to add the selenium server jar as well?