The major difference between a mallet and a regular hammer is that the former has a wooden head while the latter has a metal head. But this difference is because of the difference in the application of the two. A hammer is useful for shaping metal, driving in nails, plucking out nails, etc. On the other hand, a mallet is designed specifically for carpentry. You can knock pieces of wood together using a mallet without damaging the wood. Moreover, if you want to give a heavy blow to a chisel or a gouge, there is no better and safe way other than to use a mallet.