Keto is often used as a sort of very effective diet to cut fat preferentially. For example people like body builders use it effectively after their bulking phase.

It has gained much wider adoption recently of you include things like Atkins, but true keto is still very much more often used by a very self selected group of fitness people and a limited time (although I could be wrong and don't know of any good serveys).

However keto is not a long term diet and I don't know if long term effects have rally been studied much. I know more people that do keto cycling than sustained keto anymore.