Data creators are classes used to create data to be put into a data block, most likely to an output plug of a node. Data creators are not required for simple data types such as integers and floating point values, but are necessary for heavier data such as mesh shapes and NURBS surfaces.
The classes allow Maya to more efficiently modify and transfer the data along dependency graph connections. The subclasses of MFnData are the data creator classes. For the data creator classes that create heavier data which also corresponds to shape nodes, such as mesh shapes and NURBS surfaces, the MFnDependencyNode subclasses pertaining to the data type are used to fill the data block item with data. For instance, the MFnMeshData class is used to create a new mesh data block item, but the MFnMesh class must be used to fill the item with vertices and polygons.
Some operations may behave differently depending on the data block item. That is because these shape-related dependency node function set classes can be used to access data block items that have come from connections to other nodes in the graph as well as to access data block items that have been created locally within the node.
All operations which can return world space information, such as MFnMesh::getPoint(), become invalid when applied to data block items that do not come from shape nodes. The shape node is required to be able to determine the transformation for calculating the world space position. Caution must be used when using these methods.