Sulfate-free shampoos help retain the natural moisture of the hair so that your hair does not lose its natural shine and softness. If you have coloured hair, sulfate-free shampoos are a blessing. Unlike their counterparts, these are gentle on the hair and won't strip your hair of its color too fast.
People with dry or frizzy hair should also consider sulfate-free shampoo.
Sulfate-free cleansers maintain the natural oils on the scalp and hair, which ultimately leaves your hair with more moisture. It doesn't lather as much, which can be great if you have drier, curly hair.