Navigating in the Qur'an is not a simple matter. If you want to read up on a certain subject, the references can be found at many different places in the Holy Book. And if you moreover want to find the related hadith, you can be looking at a major effort to be undertaken, before you reach any result.
Therefore any compilation of this kind is a great help for the students of the Holy texts. This can be a really good set-off for a deeper study of any given subject according to Kitaab and Sunnah (the Qur'an and the example of the Holy Prophet, peace be upon him).