I've wondered about this for a long time. When I lather my face, I try to apply thickly enough so it doesn't all evaporate before my first pass, but not so thich that I have to watch most of that creamy stuff go down the drain, especially when using an expensive soap. Since the only soap that really does anything is the thin layer that's in contact with the skin, why bother whipping up a thick lather? I can relate to the luxurious experience of a nice creamy shave, but is there more to it than that?