This is a standard feature in video racing (driving) games and it really helps to improve your performance because you have constant feedback on how you are doing compared to a previous recording. In this case it would just show a difference between your current distance/time versus the chosen recorded workout's time at the same distance. Obviously there will be a bit of difference between recordings because of GPS inaccuracy, so it's not super-duper precision, but it should give a good enough idea without having to spend an entire race doing math in your head, or carrying a huge list of "splits" to compare to.