Mallets are usually useful for tasks that require a softer blow than a hammer, and are typically used more with artistic pursuits like stoneworking or leatherworking. The mallet allows the user to apply some measure of force to a stamp or chisel, while still giving the user control over the intensity of their swing. This is much different from a metal-head hammer that's designed to hit with as much force as possible in order to drive a nail through wood.