Skin > Edit Smooth Skin > Substitute Geometry > 
When both these options are off, your original piece of bound geometry is deleted on substitution.
When on, the original piece of bound geometry, its skeleton, and its influences are not deleted on substitution and they are placed in a new display layer. The display layer in which the old piece of bound geometry, its skeleton, and its influences are placed is named [old geometry’s name]Shape_oldSkin.
Select one of the following options.
When on, any non-skin deformations the original piece of bound geometry has are disabled and then transferred to the new piece of geometry on substitution. To re-enable the deformations on the new piece of geometry, reset each deformers node state.
When off, only skin deformations are transferred from the original piece of bound geometry to the new piece of geometry on substitution.
Specifies how rapidly the influence of joints on the new piece of geometry decreases with distance from each joint. The greater the Re-weighting Distance Tolerance, the more rapid the decrease in influence with distance. The lower the Re-weighting Distance Tolerance, the further the influence of each joint. This option is useful when the new piece of geometry has extra vertices that the original piece of geometry does not have, and you want to include them when re-weighting the skin.