The clue's in the title really. CoolerMaster likes to keep things cool, and the CoolerMaster HAF X (the HAF stands for high air flow) is the coolest of cooling cases.
This is a case you could store fresh fish in on a hot day. Only, please don't.
The HAF X is rammed with fans. There's scarcely an inch in the outer casing that isn't simply mesh hiding a fan behind it, and although the HAF X is actually very expansive, compared with Corsair's 700D the intensity of its visual design makes it seem quite compact.
CoolerMaster has made the HAF X for serious PC enthusiasts looking to build extremely powerful and thus extremely hot systems.
The design of the HAF X is almost entirely geared towards cooling, but CoolerMaster has made sure not to neglect aspects like build quality and functionality.