The other aspect of time trialing is doing something extraordinary to get a superior result. One will not excel at time trials by obsessing over data during the time trial. I use power during a time trial but I am trying to raise my level of effort, not limit it. Hence, one does not want speed, power, heart rate or any other metric to be a limiter. I use metrics to adjust effort to the degree of difficulty of the course, I put in more power climbing and into the wind and less when the wind is at my back or I am going down hill. I try to constantly increase my level of effort as the time trial progresses where the maximum effort is applied to the final 2 kilometers or so.