I eat 80-90% darkness dark chocolate whenever I feel a need to have something sweet. It's very healthy for you.
Unfortunately like Nibba said it does break some people out. It breaks me out too which is why I try to keep it to 20-30grams maximum at once. if I eat more than 50g I get multiple pimples.
So it's not as much about the calories as it is about avoiding pimples. Otherwise I'd fit it into my daily macros every day. If you can fit 20-30g of dark chocolate in your diet daily without any acne, absolutely worth doing. I can't though so I limit it to once a week.