This section is an extension of the previous section where we made multiple copies of a part on the vehicle. You chose between the clone types Copy and Instance. In this section we'll explore the ramifications of that kind of choice.
A Copy is independent of its source, but gets all the modifiers and properties the original one has. They don't share any changes down the line. An Instance maintains a connection between the original and the duplicate, and changes down the line to either will be shared. A Reference shares changes, but modifier level changes added on top of it aren't shared. A Snapshot is an extracted copy of a mesh, which rebuilds it as an editable mesh in its current state. It is used to get the state of a mesh resulting from the effects modifiers have on it. A good case for using a Snapshot would be to extract the expression or pose the result derived from combined Morph targets and Skinning.