Shift + click when Moving to new Layer

Can anyone give me some reasons why you might need to create instances of Objects on different layers?
(selecting an object, hitting M, and holding SHIFT when you click on a new layer)

I know that if you want to isolate a shadow, you must create an instance of the ground plane on a new layer and create a render layer for it (Cycles). Not sure if this is a bug, but I can’t really think of why it needs to be done.

Thanks in advance!

You’re not creating an instance of an object by Shift clicking a new layer in M, you just make the object show up on that layer too.
So for example a lamp can illuminate multiple layers.
You can do the layer management of an object also in its Object panel / Relations.

Try this:
Animating the object on one layer also transforms it on the other layer, whereas an instance (Alt D) or copy (Shift D) doesn’t adopt the animation of its sibling (no matter on which layer), unless the animation was done BEFORE the instancing.
Or: deleting the object deletes it on all related layers, but if instanced, the others aren’t deleted.

Thanks Mobimo!