1. Natures Design - Humans evolved outside under the sun. Indoor lifestyles today have deprived most of what nature intended. Regular UV exposure.
2. Sunburn Prevention - A Tan is your natural protection against sunburn increases the effectiveness of sunscreen- one reason tanners sunburn less often then non-tanners.
3. Natural Vitamin D - UV exposure to your skin is the natural way to make vitamin D levels than non-tanners.