Keto was originally intended for children suffering from epilepsy, and was quite effective for it:

The ketogenic diet is effective in substantially decreasing difficult-to-control seizures and can successfully be administered in a wide variety of settings. source

More recently it has been adopted as a weight loss tool, but it doesn’t seem perfect and especially there seems to be no reason to participate for more than a few months:

Ketogenic low-carbohydrate diets have increased in popularity over recent years, but the degree of carbohydrate restriction required to achieve ketosis remains unclear. In general, studies have shown greater weight loss at 3–6 months with KLC diets compared with LF diets, however this difference is no longer apparent at 12 months. source