There's very little that they can do that Emacs can't. It's just that if you're on the easy path, the IDE will give you a pretty high-quality experience with very little time spent configuring it. The "easy path" supports more and more use cases each year, but my experience is still that the more custom your build system is, the more likely it is that you'll not get your nice IDE integrations. That's was true in the 1990s as it is today.