HIIT has been shown by a large body of scientific literature to provide a time-efficient way to output a lot of energy (basically to burn a lot of calories).
We don’t always have time for a one hour workout or we can’t get to the gym. There’s so much you can do in 20 minutes if you use the time wisely, so HIIT is here to give you 40 workouts you can mix into own training however you like.