The refactoring tools in IntelliJ make it possible to catch a lot of things that would be very difficult to do with emacs of vim. For example, I know a certain utility method exists in several different classes, so I want to extract that method and utilize it throughout my project. The IDE will search the project for any block of code that meets this pattern and will ask you if you want to replace it with this new utility class instead. For smaller projects (<25k LOC) this isn't a big deal, as any major dev will have seen every line of code. For very large projects, I can't imagine going back.
Also, if you're basing your IDE experience solely on Eclipse and Netbeans, give IntelliJ a try. Both Eclipse and Netbeans pretty much seem unusable after you use IntelliJ for a while.