I seem to recall that at PVG, you are told to wait near the check-in desk until your luggage is scanned. The luggage goes from behind the check-in personnel on a belt directly to the scanning station that's just beyond the nearby wall, so it takes only a few seconds and an indication of the scanning results appears on the agent's screen. It doesn't slow down the process much at all. One time my bag was flagged, and I was instructed to go to the secondary baggage screening area and deal with it prior to proceeding to departure immigration and security. It was super efficient since it was a newer airport that was set up with this in mind from the beginning.