basically, the techs at bullydog test the engines and ecu and re-write some of the code to let the car handle/work/act better. for those looking for performance, the tuner allows people to add some power by adjusting the finer tuning that the bullydog engineers have worked with. you can also adjust codes and lights on your dash and understand different diagnostics while running the tuner.
ex: say you have a 2.5s and you recently installed the stillen header WITHOUT installing the 2ndary o2 bung. after 20-60 mins ur check engine light will go on. (dldjrose did this) you can go through the diagnostic menu, identify the code, and through the bd tuner, you can erase, (not delete permanantly) so that the light will not go on for a while again. till the car does its automatic diagnostic test (approx every 20 mins depending on driving)
you can also have real time updates as per a/f ratio, intake temperature, and exact digital readings of your rpm, and (i think) a proper shift time for the 6spd, and gas saving readouts along with a nice performance boost to adjust the throttle, wot, and adjust timing, the latter is used at the drivers own discretion.
this is just a basic rundown lol but i hope it helps
