I recommend you fellow forum users to this app. I am not gonna go through all the features and go on and on about how awesome it is. I've used many disk cleaning or space managing apps but nothing comes close to this. It is simply a joy to use.
For the feature-set, compared to other apps like Advanced System Care for Windows, it is expensive. But it is very simple and pleasant to use. I can't help say that "it just works".
For MacBook Air or rMBP users running on a tiny 128GB storage, this is a must-have.