@WallFlower Not wrong since other people have mentioned they like coarser salt in their batches. I just prefer the salt bars not to be that rough. Just make sure you stir the salt after the soap has thickened. You don't want a layer of salt on the bottom.
@Wandawump
The salt makes the bar very hard and they tend to last a lot longer than regular soap. I find it slightly exfoliating. My skin feels very soft after using one. Depending on the amount of salt you use, they can look like and kind of feel like rocks after using them. Very, very hard! You could really hurt someone if you threw it. The lather is different from regular soap. It's more foamy yet lotion-like. It's hard to describe. I just think they're fun soaps and relatively easy to make. I should say they're easy to make but you have to cut them while they're still warm. The hardness makes them extremely difficult to cut and they can crumble. However, they're not too hard to cut if you use a lower percentage of salt per pound of oil.
Everyone has their favorite recipe when making salt bars. I prefer a high percentage of coconut with some sunflower and castor oil. Because of using such a high percentage of CO, you have to use a higher superfat so the bar isn't drying. I use 18%-20% SF for my batches.
Other people use 100% coconut, some use coconut and a butter, some people use a recipe which is similar to a regular recipe but a little higher CO amount. Normally, salt can kill lather but coconut is the only oil which lathers in salt water so by increasing the amount, you still get bubbly lather. People use different percentages for the salt amount. I generally use anywhere from 70%-80%. Some people use 25%, 50%, 60%, etc. It's personal preference. Some people hate salt bars.
I guess the purpose is just like other soap - they get you clean.
As to benefits, I find them slightly exfoliating and they soften my skin more than a regular bar. However, this is my experience with them. I know other people have said they don't find salt bars made with fine grain salt to be exfoliating. Another member commented the help to heal minor scratches more quickly. I took this comment with a grain of salt (har har!) until recently. I had quite a few small scratches & cracks on my fingers and I was amazed at how quickly they healed when I started washing my hands with a salt bar. It burned at first but it was worth it since I kept re-damaging my hands and they just wouldn't heal. The salt bar really helped me. Several people have said they helped to improve acne.
There have been many discussions about salt batches. If you scroll through the CP section, you'll see the topics about them.