Well it's used to downshift smoother so you don't upset the cars balance, see how when you dump the clutch or let it out the cars tends to jerk back wanting to stop? Double clutching will makes your car go forward instead of jerk back. It's not used for drag racing if that's what your thinking, in drag you just upshift it's just mainly for highway battling and road racing. I"ve used both methods and they work fine for me just the second methods seems a bit faster.