It's good for those who need deadlines and like working to targets.
It's bad for those who have quite enough guilt trips in their life and don't need another one.
It's good if you need encouragement to break free of the perfectionist streak - the NaNoWriMo novel is one where the style and content is irrelevant, because only achieving the word count matters.
It's bad if you feel a failure because your personal writing process doesn't fit with churning words out.
It's good if it means your family/friends/work colleagues will give you more space to write because you can label what you're doing.
It's bad if you can only write under pressure - the ideal is to develop a regular writing routine which will enable you to continue after November. Bit like crash dieting v sensible eating and regular exercise.
It's good if you have an idea buzzing around your head that you want to get down on the page as quickly as possible.
It's bad if it distracts you from your current work in progress (new ideas are invariably more attractive).
So, NaNoWriMo might be great for you, or bad. Either way, watching this video will bring a smile to your face...