I don't have to, because a human being can easily traverse the distance in three seconds. This is why we use real life movement rates. The only time distance actually matters is to dodge explosions or in combats that take place over the range of 100-1000m. All I need to know is how fast my NPC runs and how fast my PC runs, and if they're closing in on each other or if one's trying to evade. Suddenly, I just have their relative speeds in comparison, and it's a simple subtraction of tempi or the distance between them as to how many rounds it takes to reach the person, if at all.
'course, you can needlessly overcomplicate stuff endlessly. You can assume the GM has to describe every bush and every tree in the forest, but then you're in a situation where you don't see the forest because of all the trees in the way.
Edited by DeathByGrotz