This is from my own research and experience;
pushing till you have triple extension would feel slow but you are actually
- putting your body into the right position to continue your drive/push,
- also you are actually moving faster through space with every step, and
- it allows you to continue accelerating down the track.
Getting the feet down faster is also part of the acceleration but only works if pushing is done correctly. Without the pushing element done correctly you will feel that you are actually running faster but travelling slower through space compared to the other method, and also you would reach top speed faster in the race thus having to do a longer speed maintenance to the line.