A lion has enough trouble as it is catching a gazelle, never mind if it had only three legs. If a giraffe had tiny little legs with a thin neck near the ground and a great big body up in the air it would look very funny just before it toppled over. Think of the beauty of the horse's symmetrical form and its evocation of intelligence, power, and speed and how these are linked with both the hunt, freedom to roam, and the ability to escape from danger. Symmetry is also an indication of both youthfulness and health. Human males whose bodies are more symmetrical with even length limbs are more attractive to females than non-symmetrical males.
Symmetrical flowers are more attractive to bees because they have more nectar.
Symmetrical animals tend to survive longer than asymmetrical ones so symmetry seems to be a sign of overall fitness. It can also be a sign of greater fertility. A study found that women with large, symmetrical breasts tended to be more fertile than women with asymmetrical breasts. Symmetry is also often a sign of physical health in that a blemish or defect can highlight a potential disorder or disease. Facial asymmetry is an indication of aging.