There are many different types of cleanses, but the two main cleanses that we hear about today include the Master Cleanse and the standard juice cleanse.
The Master Cleanse is a bit more specific and recommended for only short-term use. Some may say that this cleanse is a trend that may fall off in coming months.
Juice cleanses, however, have been around for a long time for reasons including health and also religious and cultural purposes. Juice cleansing is the literal process of juicing vegetables and fruits in order to gain their essential vitamins and water content in one smooth drink. It is also considered a form of fasting, since your body is missing certain key ingredients such as fiber and protein and the person is often under-satiated by the experience. Because these cleanses are calorie-restrictive, with each juice containing between 150-300 calories, you may only consume around 1,000 calories a day.
The pros of juicing include gaining essential vitamins and jump-starting weight loss in the body. The cons can include muscle loss, a slowing of the metabolism, and an onset of unhealthy eating habits (weight gain is often experienced post-cleanse).
Many of the individuals that use cleansing as a form of detoxifying or 'cleaning' the body, do so in cycles. For example, one might do a four day cleanse once a month or every two months because they feel that their body is in need of a health jolt. However, there is no scientific evidence that this process is more effective than the body's natural filtering system, the kidneys and liver.
You can see the entire process of juicing in the documentary Fat, Sick and Nearly Dead.