Once or Twice Around

Many layouts have the mainline and train traverse the whole layout once, only passing through each "scene" one time.

Other layouts, to name a few, Gorre &Daphetid, The Puffer Bridge Lines & The Coal Belt are a twice aound layout, kind of a folded figure eight, to give about twice the mainline space.a

So the question is, which is better, once around or twice around.

Thank you for your input.