I'm natural 4A and I wash with diluted shampoo once a week. Its very diluted though (1 part shampoo to 2 parts water). I may start alternating that with a moisturizing shampoo every other week (which I will dilute too).
I used to be a no-poo-er some years ago and for a while. It was nice in the beginning, but I ended up having to shampoo at least once a month because of the build-up it caused. My fine strands didn't like it so much, and I didn't use any heavy products. But I didn't use all-natural products, so I think I eventually needed to get rid of those cones, even the light ones.