Shave soaps are not necessarily used for the same purposes as bath or facial soaps--that is, removal of dirt is less important than providing a good shave. There is no agreed-upon definition for what differentiates a shaving soap from other soaps.
All soaps could be used to build a lather and lubricate one's face while shaving, but the need for a durable, moist, and lubricating lather leads to customized soaps produced to provide such qualities (qualities not necessarily needed in bath or face soaps). Shave soaps are therefore made to provide moist, low-friction lather that allows razors to glide across the skin's surface without skipping or catching on the skin, two common sources of nicks and irritation. Shave soaps may also contain products intended to soothe the skin or provide antiseptic qualities, as well as fragrances that have no effect on the shave but are pleasing to the user.