Using 3D allows me to quickly turn my concepts into realistic forms. Doing so in the early stage will give me a better understand of what's achievable,  and how far I can expand my original ideas. The main reason of choosing 3D instead of 2D is because of its flexbility – I can have the same 3D model/scene render in many different styles. If later on I discover the style doesn't quite meet the audience's expectation then I can change it without having to redo much work.