Shifting technique can make a big difference in lap times. I’ve seen bad shifts take as much as 1.2 seconds on an old H box. Good shifts in a new BMW - .4 seconds! The delta of .8 seconds is time that you are not accelerating and maybe even decelerating. A good working transmission and tight shift linkage can make a big difference to quick laps times.
We all know that we’re supposed to go from throttle to brake quickly, but many times this doesn’t happen. And we are not talking about the a high speed corner with a lift, we’re talking about an end of the straight hairpin or other medium to low speed corner. This is when the little bits of coasting can cost us lots of time.