driveing the car in auto allows the transmission calibration to shift for you taking in account a number of things such as load, speed, throttle input, traction control on/off etc.. and is designed for a smooth ride or shift and not necessarily performance. In the stick mode most of these inputs are over ridden and allows the driver to control revs and shift points which will equate to quicker excelleration and snappier throttle response in passing situations etc. My wife drives the XF the most and leaves it in auto but I use it alot when I drive .