I just gave this a try and slowed down by 50% using a 3rd party tool and you get used to it too easy and fast. This should only be used for learning some new movement that you were not familiar with but nothing else ie. racing, because your brain will adjust too quickly and you get used to something way too artificial (your reflex time virtually halfs) which is not the case in reality and normal speed then will feel super fast :p
So yeah it's maybe not as useful as I first thought.