This is usually set to true only when HandlesChildren is also set to true. When this is true, GenerateChildAttributes and ConsumeChildAttributes will be called for each child object of this transformer's (parent) object.
This property is infrequently used; but it is very handy when you want a "parent" object to associate attribute values with each "child" object, but those attributes are not properties on the "child" object. The only pre-defined use of this property is to help save bounds or path information for each node or link inside a collapsed subgraph.