It is more than fine to only wash with conditioner, BUT you should use clarifying shampoo every 2-4 weeks to prevent product buildup if you use too much product and products containing silicones. Also, expect a transition period in which your hair will be greasy some what until it gets used to not producing as much oil due to the drying of shampoo. If don't want to use shampoo, you might want to consider a baking soda or ACV rinse to clarify.