When drive-by-wire throttlebodies became a thing a few years ago, manufactuers started adding torque management calculations to ensure that the powertrain isn't exceeding it's rated specs. The idea is to reduce over-engineering while maintaining reliability and reduce expenses of warranty claims from those blatantly abusing their cars. As an example, transmissions are noticeably less robust in their input toque ratings but doesn't matter when the engine is programmed to never exceed it.
Previous to this, engine computers were simpler and simply did their best to keep the air/fuel ratios within spec. While gains were permanent back then, custom tuning was still the only way to get the most out of a setup.
With torque management, any mod that increases the amount of air going into the cylinders will be nerfed. With turbo motors this will be done by reducing boost. Not sure with NA motors, reduced commanded throttle %? Exhaust mods should be less affected.
