Duplicity with Instance Objects
Maya 2012 Tutorial
How to Create a Single Object that Affects Connected Instance Shapes in Maya
Imagine creating one object along with two instances of the same object. As you reshaped the first object, the others were reshaped as well. The trick with instances is that they copy the initial object at the component level. In other words, if you scale the original object while in the Object Mode, it has no effect on the instances. Once you switch to the Component Mode, the instance objects are modified.
In this example we will add a polygon cube to the workspace, then make two instances of the cube. As we reshape the original object, the instances will also be affected.
Add a polygon cube to the workspace by choosing Create > Polygon Primitives > Cube (include options).
In the option set the Width, Height, Depth and Divisions to 1. Click Create to add your cube.
Select the cube and choose Edit > Duplicate Special (include options).
Select Geometry Type: Instance,set the Translate x to 3 and Number of Copies to 2. Click Duplicate Special to add your instances.
Right-click the first cube and choose Vertex.
Using the Move tool (w key) move the vertex and notice how the other objects are also affected.
This is a great way to model symmetric objects such as a face. For more information, see topic, Symmetric Modeling with an Instance Object.