What is the meaning of butterfly light in photography? What are its advantages and disadvantages?

Symmetrical lighting and butterfly lighting, commonly known as butterfly light, are a special way to use light in portrait photography. Butterfly lamp, in a sense, is an inclined ceiling lamp, a way of using light in front light or in front light. The method of arranging lamps is more suitable for westerners and people with clear bones. The usual arrangement of butterfly light is that the main light source is above the optical axis of the lens, that is, right in front of the subject's face, and it projects to the human face at 45 degrees from top to bottom, and casts a shadow under the nose, which looks like a butterfly and gives the human face a certain sense of hierarchy. Butterfly light is mostly used to represent women. After this light hits the model's face, the most obvious sign is that it will produce a butterfly-like shadow under the nose.