Paste Remembers Layers (found under the Options menu of the Layers palette) does exactly what its name implies. If you copy an object from a Layer and paste it, Illustrator will “remember” what Layer that object is from and paste it in a Layer with that same name in the document or in another document. If you paste into some other document that does not have a Layer with the same name, Illustrator will create a new Layer with that name.
If you deselect Paste Remembers Layers and select several objects in different Layers and then Paste them, all pasted objects will maintain their original stacking order but will end up in the currently active Layer in the original document or any other document.
Tip provided by Jeff Witchel, Certified Adobe® Training Provider.