Interesting questions, Kerry. Good topic!
(And, to misquote you,) I think you're right in saying that the importance of layers is taken for granted.
If I read it right, you're not looking for the procedure on how to do it, but asking hypothetical questions, like 'How can this BE?!'
I've tried to explain layers to Non-CAD folks before and the best way is to show them a set of transparencies that, when stacked, show an image in its entirety, then break it down and show them each transparency individually, only containing certain parts of the image. Then, I see the understanding dawn on them and everyone's on the same page.
My perspective:
Copy to new layer would generally be a No No in our office, but not unheard of. If an entity could theoretically 'fit' on multiple layers, I would rather see a single instance of that entity on a layer that has a broader coverage. For instance, imagine layers, "Numbers" and "Letters". On which layer would you place the string, "Eight"? Although a stretch, it could fit on both. Instead, how 'bout we just make a layer called "Text" so we can just...
Move the entity to the correct layer. This makes it easier to manage when the time comes to change "Eight" to "28". Just throw it on a "Text" or "Annotations" layer and you're golden. No copies floating around to bloat the file size.
Is there a common belief that objects reside on Layers, resulting in it being taken for granted that the Layer is the repository ?
I guess one could argue the fact that the layer an entity is on is not the repository for the entity, but a property OF the entity. However, I like what CAB said.
...when objects did reside on a particular "Layer" of trace paper? Then to change the Layer meant "Moving" the objects to another sheet.
That statement makes the "Layer" more of a "Repository" than a "Property".
I think layers had more definition and meaning in manual drafting than they do in CAD.
Speaking of CAD... I've got some to do! Back later!