It is a short term way to break through a weight loss plateau or to help you get back into ketosis quickly if you are on a ketogenic diet. It’s usually just a short period of time like 3-5 days. It is not recommended to do longer than that as you are at risk of nutritional deficiency.  Essentially you only eating eggs, healthy fats and cheese so it’s a temporary restrictive diet but again you are only following this for a few days.