It'll provide similar benefits as writing your own text editor (which was suggested here).
It can also provide type hints and type checks for dynamically typed languages, thereby making them more like statically typed languages (also suggested in here).
Plus a good IDE will speed up searching as well as index the source code to make things click-able, thereby making large code bases or dependencies easier to navigate (also suggested in here).
So basically you can get a large chunk of the improvements that others have suggested in this thread simply by purchasing a good IDE :)