A good aid for winter starting in particular though..full advance for the first start in cold weather,back off half once started,ride for half a mile,back off to where it sounded happiset at speed or up steep climbs...riding the old 'flat tank' veteran bikes..ala Banbury Run or London To Brighton is a real challenge,some had no actual force feed for the engine oil,so you could in a 30 second period be hand changing gears,opening/ closing throttle lever(not always hand twistgrip throttle),adjust advance /retard lever,adjust rear drive belt pulley,(belt drive not a modern thing),pumping oil with separate plunger to engine,all whilst watching well ahead for any idiot car drivers pulling out,as many bikes had little better than bicycle size rim brakes..!A real juggling act..