Ketosis has worked very well for me in all areas
I've been doing a ketogenic diet for close to 8 months now (basically similar to the Wahls protocol with Brain Octane and a lot of vegetables) and I've found that my lean muscle gains are better than they were when I was on basically a standard American diet. I don't know whether that's from working out harder during workouts or otherwise, but I consider the results to be very favorable. I'm 6'2" and 225 pounds with a six pack now clearly showing (but perhaps still not showing enough but it's certainly getting there for the first time ever).
Even if I found that I was losing lean muscle gains (again, definitely not the case) I would almost certainly stick with the ketogenic diet. I sometimes fall out of ketosis and I generally don't worry about that much now as it's quite easy to get back but sometimes in eating out there will be hidden sugar in what I order and I try not to obsess about that. My HDL went up and my triglycerides fell dramatically (LDL was slighter higher), as did my CRP and HBA1c which is very positive. Fatty liver disappeared as did my prediabetic diagnosis (I was shocked by the diagnosis as I had no symptoms for either condition that I was aware of at that time). Strangely one of the most noticeable differences was that my fingernails changed from dry, brittle and weak to shiny, hard and strong -- they used to chip regularly and now it feels like they could cut glass. I also found a major change in energy levels and overall cognitive functions (I rarely forget small things now which used to happen to me quite frequently).
I have no idea if ketogenic diets work for most people and I understand from the research (Dr. Attia and others) that some people (rarely) do very poorly on it. But, it works incredible well for me and my recommendation would be for everyone to at least try it for a month. I had a difficult time adapting for the first three weeks and during that time my workouts were terrible. I was weak and I tired out basically immediately but once that period past everything changed. The only major thing I found after this initial three week period was that one crossfit/bootcamp workout a few months ago left me nauseous and wanting to violently throw-up but I think that was due to the typically sodium deficiency since I started supplementing sea salt daily after that based on the literature and that hasn't ever happened again.
I see a number of posts here (particularly by Jason Miller) that say that carbs are absolutely required for athletic performance in general and for bodybuilding in particular. That may be Jason's experience but his comments imply that this is a certainty for everyone which is clearly false in my opinion.
But, don't rely on my opinion -- check out youtube podcasts by Dr. Attia, Dr. Volek, Dr. Phinney, Dr. Wahls, Dr. Westman, and even Rhonda Patrick. For more athletic performance and bodybuilding related check out Dr. Jacob (www.bodybuilding.com) or Dominic D'Agostino. All of them are either M.D,'s or prominent medical researchers and each of them will, unlike Jason Miller, tell you that in their experience this works for most people but certainly doesn't work for everyone so in that regard it is important to find out on you own what works for you. For me, I've found what approach I believe I'll always continue to use.
There are a number of variants on ketogenic diets just as there are for carb-based diets. If you eat only Canola oil you'll be in ketosis but no one would consider that healthful. I used to crave sweet and thought that I'd never be able to give up on them. Now the thought of sweets is more likely to make me ill than to initiate cravings for anything of that nature. This took time but it gets easier every day.
Good luck to everyone that tried this approach. I believe what many of the above referenced M.D.'s and researchers appear to advise on, that being that keto adaptation is a moving target and although initial adaptation happens for most people in about 2 weeks the more fulsome benefits they comment on are more likely to emerge in 18 to 24 months.