I have been doing IF for a while with decent results.
Here are a few of my thoughts on it:
I started it in order to lean up and to my surprise I have lost fat and continued to gain strength.
It works for me because I rarely have an appetite in the morning and being in the business world I often have lunch and dinner meetings. If I had a big breakfast I would easily end up over my macros if I ended up going out for lunch and dinner meetings. Sure, I can be selective with the menu but if I am at Morton's, Gibsons, Ruth's Chris, etc, I sure as shit will not be ordering a salad.
Sometimes I work out in the mornings @ 10am fasted except for EAA's, PeptoPro, etc so those days I am really not 'fasted' (from protein) very long in comparison to a regular diet when my first meal would be 8am ish.
In another thread someone thought this method is for lazy people that don't want to fix 6 meals a day. Maybe, but I don't fit that mold. I will fix my own meals or have someone fix them for me. I have a staff at the house and an executive assistant. I could have 30 meals a day prepared or delivered for me if I wanted to.
With all of that said:
I'm not a mass monster like most of you guys. 5'6" 195 so my macros are much lower than most of you. For you big guys, I just don't see how you could get all of your macros in 8 hours, especially if primarily solid food.
I agree that it is not the most efficient way to build muscle as quickly as possible-no way it can be.