not to mention that how much fat you burn isn't all that relevant. You want a negative calorie balance at the end of the day. That's your goal.
in theory, burning fat (from body stores, not dietary) might be a good thing sometimes. Say you're gaining weight at a very slow pace so you're in a surplus (IE, you're not losing fat off a deficit in your diet) and you exercise a lot of middle intensity to burn fat off your body. That might help you lose fat or just stay lean through your bulk. Since if you did cardio to take down your glycogen stores (of course, all cardio burns fat aswell, but you get my point), that would just get refilled and wouldn't drop into your fat deposits since you're not in a deficit.
But then the whole fasted cardio is shot to **** when in trained men, some research has shown (like g8r80 pointed out) that fat oxidation isn't increased in a fasted state (using low and middle intensities, but who does HIIT on an empty stomach?).