So in the standard throttle mapping your car might hit 80% throttle at 50% pedal travel but with a throttle controller you can program it to be even more responsive, like 80% throttle at 25% pedal travel. But it can’t exceed 100% throttle.
More throttle doesn’t damage the engine since it never exceeds 100%, but for most people fuel economy will be worse if they use more throttle, but it’s no different than simply pressing the gas pedal more.
So it’s more of a quality-of-life mod that just makes it easier to reach full throttle with minimal gas pedal effort, if that’s what you want. It may give the impression of making the engine more powerful but it doesn’t do that.