I know there are many varying view points here, just chiming in based on my experience. I have done keto before as part of my bodybuilding prep last year, and IMO it is not sustainable or healthy to do for an extended period of time, but I do think it can be a very helpful weight loss tool when implemented properly. Our bodies and brains are meant to run on carbs, I think doing a permanent 0 carb, 0 vegetable diet is not healthy or sustainable. It is most definitely helpful for weight loss, I've found some people respond better than others to a keto diet. I recently put a client of mine on keto for a few months to lose some very stubborn weight, he used to be diabetic and has a family history of it, was extremely carb sensitive. We put him on keto, he lost more weight, now we're slowly getting carbs back in.
I think a more moderate carb approach, even if they're just from beans, veggies, etc., would be more sustainable and healthy. I can't imagine any situation where eating only meat and fats, and not vegetables, is a good way to go.
Training was very challenging on 0 carbs, brain fog (even after the transition period), I told my coach if I had to do keto to do bodybuilding, I wasn't go to compete anymore.
That's just my experience with it. I know some people do keto as a more permanent diet, but even those, like @dchris, have carb refeeds. IMO doing a more consistent, low carb approach would be smarter and healthier than permanent keto.