Also experienced professionals still need to stay in shape, especially with the rhythm. The very first requirement for a musician is to be able to imitate sounds. You hear sounds in your imagination or from the outside world. You should be able to replay those sounds using your voice or an instrument, and this is the real task for any player or composer. Technically this is what making music means.
Musicianship starts here.
A professional musician, especially one with the perfect pitch may consider this as childish. In fact even a pro should strive to improve the ability to memorize and replay sophisticated rhythm patterns. This contributes a lot to better musical phrasing. It doesn't make sense for somebody to learn how to read music or play a musical instrument, and not be able to imitate sounds with the voice or the instrument. The author of this program has plenty of experience and I can assure you that the attentive ear can be improved to the highest levels, even for someone considered tone-deaf.