Probably not many downsides, to be honest.
Just things that lead directly from the action itself, like
- you can’t eat things whenever you like
- you have to fit everything into 1 hour
The benefits are
Your body is forced to be efficient and use food you give it, when you give it.
You have less opportunity to eat things that you didn’t start the day off intending to eat.
You will quickly develop the ability to defer and ‘say no’ to desire for things, as you get used to putting them off a long time.
Build self-control and delayed gratification.