Most bikes have electronic quickshifters where the rider still manually changes gear with his foot while on full throttle and the electrickery kills the ignition for microseconds at a pre set up/programmed time while the gear changes, the pop/bang noise ids the unburnt fuel being ignited afterwards. I don't think they are used between 1st and 2nd as a quickshifter set-up does put a little extra stress through the chain in the lower gears as J McG found out leaving Ramsey a few years ago when he snapped his chain. Back in the day before quickshifters and electrikery a rider would just "knock" the throttle ever ever so slightly when changing gear - the clutch would not be used in this manner either.