Nowadays an increasing number of people limit their consumption of animal products. Although this is a fairly recent phenomenon, vegetarianism already exists for a very long time.
As for nutritional value, a vegetarian diet provides more complex carbohydrates and fibres (through wholemeal products) than the traditional western diet, which contains more high-calorie foodstuffs, (saturated) fats and cholesterol.
Numerous studies have demonstrated that vegetarians have a healthier lifestyle and are in better shape than people who eat meat. They suffer less from obesity, their cholesterol level is lower and they are less likely to develop high blood pressure. They are less sensitive to allergies and less susceptible to cancers.