Most fuel injected vehicles will see gains with a tune because factory settings are not performance oriented. Tuning of a fuel injected vehicle is achieved through the PCM as timing, fuel and air parameters are processed there. How much is dependent on what the hardware can support and how much the factory left on the table. Adding performance parts like headers will increase the potential for gain. Changing the jetting, timing, and air input on a carbd motor will have the same effect.Slightly academic question but....
Say the exhaust was changed - headers and/or better flowing system downstream. Reading the posts that would demand a re-tune to make the most of it. Is that for fuelling more than ignition timing? Would such a change require tweaking of the ignition timing? And, if it were a carbed motor, would the carb cope with the exhaust changes without recalibration?