The technique you use to copy an element depends on where you want to place the copy. When the copy will be placed far from the original or in another document, copying and pasting it is generally easier. When the copy will be near the original, duplicating is can be simpler.
You can also select the element and choose Edit > Duplicate (from the Edit menu at the top of your screen). The duplicate appears on top of the original, slightly offset. Drag the new element to the desired location.