The main advantage of CAM photosynthesis is that it allows only minimal water loss during hot, dry days. This type of photosynthesis is commonly found in desert plants. Plants using other methods, particularly what are known as C3 plants, are unable to photosynthesize sugars under such harsh conditions.
CAM photosynthesis still relies on taking in carbon dioxide to generate sugars, but plants cannot open their stomata to take in this gas without also risking water loss. CAM plants deal with this by only taking in carbon dioxide at night, when conditions are relatively cool and humid. They then store the carbon dioxide in the vacuoles of individual plant cells as acids. During the day, when sunlight is available, the plants close off their stomata but can use the stored carbon dioxide for photosynthesis. The amounts stored are often very limited, however, which restricts the rate of growth of these plants.
Plants that perform CAM photosynthesis deal with water loss by separating their photosynthesis by time. Plants that perform C4 photosynthesis are also able to deal well with somewhat dry conditions, although not as dry as CAM plants can. They do this not so much by protecting against water loss, but by minimizing the consequences of water loss.