[acammer]

One of the biggest reasons to use a 2-step is consistency. It obviously has a place for building boost in turbo cars, but it's a great tool to help get the same result, time after time, no matter what the aspiration (natural, turbo, nitrous, etc). With a 2-step, you eliminate a couple variables in the launch sequence - you have a consistent RPM, and a consistent power setting (usually wide open). With those two variables "locked" you now have something much more repeatable, and you can dial that launch RPM up or down to suit track conditions.

With a more powerful car, it's often going to be used in conjunction with some other forms of power management (ignition retard, boost ramp, etc), but the idea remains the same, you're eliminating driver controlled variables and locking them in, so you can get the same result every time.

You can use a 2-step with a trans brake car, foot brake car, and even clutch cars. I love seeing them used for those purposes. And I HATE seeing them used for "pops and bangs" at the car meets where not a car in sight has ever taken a starting line.