Back when I was 13/14, I was allowed to taxi aircraft about the airfield solo for a multitude of purposes having completed 2-3 hours of actual flying lessons and well before my first solo.
When I could see everybody was busy, I always crossed my fingers that somebody would pipe up and say to me... "Say, would you mind bringing ZN over to the pumps?" Or similar.
As far as practical value goes, it does get you used to the idea of being in a moving aircraft with nobody else onboard, and it's easy to forget how fun it is being given that responsibility so early on in training and, in my case, years
