It is important you clean your hair regardless of what types of products you use. Scalp skin, just like any other skin on the body, must be kept healthy to ensure a healthy body and healthy hair production. If the scalp is not cleaned regularly, by the removal of dead skin cells, toxins released through the skin or external hazards (such as bacteria, viruses, and chemicals) may create a breeding ground for infection.
Washing hair removes excess sweat and oil, as well as unwanted products from the hair and scalp. I recommend shampooing 1x-2x per month.
If you decided to say good bye to shampoo, that’s fine, but make sure you avoid very thick products with silicone and glycols. The only way to remove these products from the surface of your hair is with a shampoo.
Co-Washing your hair is great because conditioners can also provide a physical layer of protection for the hair against physical and environmental damage.
Sources: “Hair Care” Wikipedia.org