Rigid skin point weights
During rigid skinning, for each rigid skin point (for example, each CV of each NURBS surface), Maya assigns a rigid skin point weight that controls the influence of a joint on the point (for example, the CV). By default, each joint can influences the skin points of its nearest skin object equally, but you can edit the amount by which a joint can influence a skin point.
The main difference between rigid skinning and smooth skinning is that in rigid skinning only one joint can influence a particular skin point (CV, vertex, or lattice point), but in smooth skinning, many joints can influence the same skin point. Because smooth skinning allows many joints to influence the same skin point, you can immediately get smoother deformation effects right after binding skin.