Copy/Paste vs Export Selection ...
 

What are the pro's and con's of copy/paste vs export selection?

as far as i know there is no copy/paste function in Maya but an immediate thought would be you cant reuse the asset at a later date since you wouldn't have a .mb file to import.

There is a copy paste... but I would stay away from it. You end up with geometry (and I have seen this before) called pasted_pasted_pasted_pasted_pasted_pcube01

Not sure the details of export selection, but I'm quite confident this is the better way.

As stwert mentioned, you get pain in the ass names, plus you can use export various filetypes(.obj, .fbx, etc) with export mode.

cheers,
Chris