Because i know what im doing both fuel and timing side of things. My last setup was not damaged due to my tuning although if i had the safety features enabled that i didnt know wernt it might have saved the damage but more than likely not. It was a big issue with my fuel pressure regulator.
I have no doubt i could tune the car myself but again wanted the help of a professional who is used to tuning high hp cars because I didnt want to take any chances. As for drivability and out of boost, that is easy as hell to tune.