Is it beneficial to have WTP? Which features are most useful?
WTP stands for Eclipse Web Tools Platform. It adds support for Java EE development, such as writing web apps (using JSP, JSF, etc.), writing EJBs and writing Java web services. It also includes tools to allow deploying your app to a Java application servers, such as WebLogic, JBoss, Tomcat, etc.
WTP also includes XML and JavaScript tooling that might be useful even if you don't intend to do any Java EE development.