Dairy products contain protein, which is a necessary macronutrient. However, just as some people are more suited toward eating red meat and some are not, some people can handle more dairy products than others.
First and foremost, all dairy products that one consumes should be organic. If your body is suited to dairy products, then once per day is adequate. I eat yogurt nearly every day, but I have essentially eliminated cow's milk from my diet.
For many people, dairy products such as cheese and milk products are the direct cause of symptoms like fatigue, nasal congestion, colds, arthritis, bowel disorders, and allergies. If a person has any of these symptoms they would do well to eliminate dairy products from their diets.