We must have the choice of exploding a group of objects that are, by default, cast into the virtual Group by Instancing. Decoratively, iif you change one you change all of the instances. This practice can greatly reduce the Geometry load of a scene. Useful in recreating the Acropolis's many columns.
But...
If for some artistic reason you need to change the Shader on an individual column, you must first, remove this geometry from the hierarchical instance or Group.
The ideal, is to be able to fetch one single item from an Instance, and make it the top node of a new hierarchy so that it may be Shaded as required or placed in a new group, or topologically modified.
Currently I find it impossible to fully extract/remove an instance member from the Instance.
Maya has the ability to do this 'explosion of an Instance' - or at least is did back in the A|W days.
David B Fisher