Co-washing short for "conditioner washing" is a process of washing or cleansing the hair with a conditioner as opposed to a shampoo. Many naturalistas resort to co-washing because it does not strip the hair of natural oils like most shampoo's which contain sulfates (cleansing agent found in detergents and dish washing liquids).
Curly hair is dryer than straight hair because the circular form of the curl pattern makes it harder for the sebum produced by the scalp to be transferred to the hair shaft. Co-washing aids the hair in providing additional moisture and is great for excessively dry hair.
If your only means of cleansing is to co-wash this can cause a problem and potentially affect growth. The purpose of cleansing the hair with shampoo is to get rid of product build up and excess debris that can clog the pores. Conditioners should never be applied to the scalp because they are usually designed to be heavier and thicker in consistency (excess build up). With that said, co-washing is not bad but it should not be your only means of cleansing your hair. If you are a heavy co-washer you should wash with a regular shampoo at least once every two weeks.
Ways to tell if your hair is over-moisturized and you NEED TO STEP AWAY FROM THE CONDITIONER:
Strand test: Take a strand of hair. Hold both ends (root to tip) and pull. If the strand stretches and then snaps or coils up on the ends it is time for a cleanse.
Touch test: If your hair feels gummy like the tasty gummy bears/worms. It is time for a cleanse.