Well I'm not arguing it has its merits, but it just seems a rather pointless exercise unless you absolutely have to do it due to your lifestyle (work not allowing you to eat or other time restraints).
Trying to eat the amount of calories you need too in a small window is just daft, it's uncomfortable for a start, I was struggling to eat sometimes I was so full when eating all day, let alone when I have to eat so much in a restricted time period. Also, because of this, you'll cut out a lot of foods that are important, you might not eat enough veggies as you don't want to fill yourself up on stuff like that, instead concentrating on more calorie dense foods.
And training fasted, I don't care who you are, you're not going to be training to your full potential without eating for so long, you're going to lack the intensity you need to really have the gains you want (and if you don't train fasted, you're missing the point). So doing it in a plan to gain mass is a silly idea. And if you're doing it to lose weight, why put yourself through it? You'll have much better results eating smaller meals more regularly throughout the day and training on decent meals.
A calorie deficit is a calorie deficit, how you achieve that doesn't make the slightest bit of difference. So if you want to lose weight, follow a decent diet and workout plan with some cardio thrown in and you'll see better results.
There's a lot of other reasons that make it silly, but it will just explode in to a bro science debate as peoples beliefs vary so much on this sort of thing