Well the real PSMF is a clinical protocol for morbidly obese patients. It's used for people who get gastric bypass surgery AFAIK. Lyle's version includes weekly "refeeds" and other modifications but it's still a very drastic measure (which he admits). It's the type of thing someone might do if they were a bodybuilder who was behind schedule in dieting for stage and desperate to lean out before the show. Horrible if you are interested in maintaining strength, obviously. Izzy (Tom Narvaez) did it for a while, there's a video somewhere on the Powerlifting to Win youtube channel if you're interested.