It is the "batteries included" version of Haskell that comes with basically everything you need to write production ready software. There are obviously a lot of useful packages on `cabal`, but they are mostly useful so that you don't have to recreate the wheel (or want to do web-dev).
It's also meant to be used as a reference for distro package maintainers. If your code builds properly with the current platform, you can be confident it will build properly in most systems.
Edit: Let me rephrase my question: Is this for someone who would like to start learning Haskell?