Ever wonder why your skin feels so dry after using a commercial soap that says, "moisturizing" on the label? Here is why, glycerin is a natural by product of making soap (combining oils with lye). Glycerin is very special. It is a humectant which in plain English means that it draws moisture from the air. So if you bathe with soap your skin is coated with glycerin and therefore draws moisture to your skin.
Commercial soap makers discovered that instead of leaving the moisturizing glycerin in the soap they could remove it and sell it as a separate product! Now from a business stand point that it great, double the profit from one product. Plus, now you need to buy lotion because your skin is dry.
Handmade soap is different. The glycerin is left in and a lot of the time extra is added. Those who experience the rich smooth moisturizing lather seldom go back to commercial soap.