Another advantage of a standard-ish circuit, is that the focus is on preparing for the final turn -- you aim to have your final turn completed at a safe height (and speed) in a reasonable place.

There's no reason you can't do this in a 180 deg turn too, but my guess it that it somewhat reduces this focus if it's not trained well. It could potentially have you focusing on your reference point too early, flying more cramped-in circuits as a result?