Originally Posted by
kensuf
You don't need accurate speed. I think accurate power and HR is very very very useful for pacing yourself, but speed is isn't really helpful.
I think BTS is referring to CdA calculation. Accurate speed is required/essential.
With respect to training and racing, power is ones currency to buy speed. Racing is all about speed. Hence more power is good but reducing the cost of speed by reducing CdA and rolling resistance as well as drive train losses is important as well meaning one can purchase more speed with less power.