It's for Max Power. Fuel efficiency goes out the window cause you need to get moving as fast as possible. Stomp and hold until power is no longer needed.
It will downshift to get you in the max power band (higher revs to get you moving) and continue to upshift at or near redline until you get off the switch.
It will not damage the car. Harder on it, arguably, but it won't let you overrev and cause damage (in the auto). Even in manual mode it won't let you downshift if you're going to overrev it. And if you run the revs too high in manual you'll ping off the rev limiter.