I am a believer that these quick diets are extremely bad for your health, and should be approached with caution -- and that cleanses can also be dangerous unless you are extremely careful.
Any 'diet' that causes collapses, extreme fatigue and puts the body at risk is not a good diet and shouldn't be suggested for anyone to use.
While cleanses can be quite safe IF you are careful and IF you are already healthy and have a stable diet, the shouldn't really be used as a weight loss tool, or even done while dieting. When dieting, your body may be under a lot of stress... adding a cleanse to that is just asking for health consequences.
Then again, I take dieting advice from celebrities with a grain of salt. Often times, a handful of it.