It would be huge for me (the fact having the benefit, at least), it’s about the biggest deficit I ever could do long term (counted from fat-loss, my body is simple like that. I surely didn’t lose much muscle)! I was very happy with that.
But it’s not for everyone. I experienced absolutely nothing. I ate the same on keto and stalled the same (and I knew for a fact that I can’t keep my body with less energy. I mentioned my body being simple regarding these things, it’s helpful). When I started to eat about 200 kcal less and much more carbs, I immediately started to lose fat after not losing any on keto and it continued for long. Later I went back to the original intake on keto and never lost fat, not even when my weight became the same again.
It’s very difficult and I have little data and only one not always exactly the same body but as far as I can tell, my energy need is the same when I am in or out of ketosis (my activity is usually the same, my weight is usually the same and my body loves its fixed numbers). I have little info about me on extremely low-carb but it seems it is the same. But I will need stable fat-loss to figure it out, hopefully it will happen in the near future (but as I am not the same person as in the past, I would need to lose off keto too). Oh whatever, I am not even sure I will keep tracking.
My body does waste energy when I overeat (I’ve read it’s genetic, not super uncommon but most people don’t have that. maybe it’s different on keto, the genetic thing works on any diet. it definitely did on high-calorie HCHF for me), that’s why I ate a ton on high-carb and very very slowly gained. Once I tried it out, I raised my calories by 1000 kcal for a month (not intentionally, I was hungrier then), well it’s a short time but nothing (and no more activity or diet change). It’s nice but it can’t help me at fat-loss, sadly. And I suspect it changed its policy lately and I gained when I went a bit off, nothing like in the past when I gained nothing. Oh well, human bodies, all are different and subject to change!
Sorry if I got carried away or if it’s not for this topic, I can’t even decide it now.