It's how they are tuned to be "fun". They might make the engines extra noisy for a second after you hit the throttle, so it makes an exciting "zrooom". Performance can vary with speed - at low speeds, after you've been driving a few minuets, they might go into racecar mode. At higher speeds, or when you are just starting driving, they'll re-tune for safety.

Basically, the car should "feel" responsive. When you change what you are doing (i.e. accelerating) it should respond with a lot of gusto. The trick is, not doing this when the driver doesn't want it.