It all depends on your objectives, really.
By eating low carb I fixed problems with blood glucose levels in days, and then lots of other things improved, and I eventually realised that I had lost quite a lot of weight - I had become just enormous on the grains and low fat diet the GP and his minions insisted I follow.
In the past I have tried low calorie diets and all failed, but for some people they work all the time they are losing weight, but there is no follow up with advice on maintenance levels and methods to keep the weight stable. I must have gone to most of the diet clubs at one time - I threw out a huge heap of literature, recipe books and glossy brochures a few years ago.