Controlling smooth skin weight normalization
When you are changing (editing or painting) the weights of smooth skin objects, changing the weights of one object can affect the weights of other objects. This is because Maya considers the weights of all skin objects being influenced by a particular influence object as being relative to one another. Maya does this by requiring that all the weights add up to one. When you change certain weights, Maya can automatically change various other weights so that the total of all the weights continues to be one. This allows Maya to know the relative influences of the weights.
The process of scaling numbers so that they all add up to one is called “normalization.” By constantly normalizing weight values, Maya keeps track of their relative influences.
Maya normalizes smooth skin weights by default, but you can control whether a smooth skin object’s weights are normalized. You can disable weight normalization, and also enable it again. Also, if you’ve changed weight values with normalization disabled, and then decide to normalize them, you can do so.