Just a thought.... if an airbridge is used and the flight is boarded strictly by seatrow(ie rear rows first)..at most airports... it will normally be far..far.. faster than using buses provided enough time has been given to to make any gate changes and get the pax (unless its free-for-all seating) , bags ,catering,fuel etc to the correct gate on time .... if it involves a terminal change then the opposite will probably apply IMHO...