In the winter months I usually test the athletes I coach every three or four weeks. There are several reasons for doing this. The first is to establish training intensities for workouts. I'll use some mix of these measurement methods to set the training zones every day. I also want to gauge progress within and between seasons.
Fitness is never constant.
It is always changing, either for the better or the worse. By setting some baselines with testing we have a quick way of measuring this change without the need for a race - the ultimate test. Sound test results also allow the athlete to make the best use of limited training time as testing eliminates much of the guesswork. After setting and regularly checking the intensity zones, I can schedule a workout based on the athlete's most recent information. This means that every minute of training is done at the right intensity.