I've never done super full keto (as in almost zero carbs) for over like a week, but I ate way lower carbs and lots of meat/fat for my calories.
To put it simply. It was terrible and I pretty much lost a year of athletic performance from doing that.
Initially, you might feel pretty awesome at first. Because you're sorta "high" on catecholamines, which are adrenal hormones (note amine, think of other substances that end in amine...) But eventually you'll pretty much crash because your adrenal glands will be on basically high alert all the time.
But anyway, my specific experiences, in athletic performance, your endurance is affected, your, say, 1 rep max type of strength isn't really. Worse though, it can be pretty bad running on such a diet doing things like, say, driving, as you'll pretty much be tired and irritable all the time after your honeymoon period is over. Eventually you start replacing carbs with caffeine. Then you're like "wow I'm miserable" and think "Oh, it can't be the fact I've not been eating like any carbs" and this continues until you stop doing the low carb thing. Your nervous system runs on glucose, no glucose, no fun. Carbohydrates are also needed for seratonin, no carbs, low seratonin. Even if the diet physically allows you to be all right, mentally you'll be trashed on the diet after the "honeymoon."
For me specifically, I was 195 during my low carb days, and on a 3000 calorie high carb diet with relatively low fat, I dropped to 182 relatively quickly. It MIGHT be all right if you plan to just use it to cut down 5-10lbs quickly (so you don't go past the honeymoon.) When I told a bodybuilder at my gym about my low carb, he said "yeah, that's for if you're at like 8% bodyfat and wanna go to 6%." Which I think is pretty accurate in their usefulness. Also, I'm wondering if I've messed my hormones up a bit doing low carb or not. Overall, just terrible. I'd say don't do it.
http://anthonycolpo.com/why-low-carb-diets-are-terrible-for-athletes-part-1/Good article to read.