Not to be argumentative, but for certain desired outcomes, it works great. Seems that the longer you do keto, the quicker your body goes into ketosis. That's why the Metabolic Diet and TNT diets make you do straight keto for at least 4 week, because then once you break keto for a day or so, your body can get back into it quicker. Insulin is a muscle growth hormone, and it is release as a response to carbs. As I understand it, keto puts the body into muscle-loss zone. It helps to break it by creating an insulin response occasionally if you want to gain/preserve muscle.
But agreed, if you have lots of weight to lose, don't break keto. If you're trying to lose a bit of weight without losing muscle (or possibly even gaining muscle), carb cycling is great.