Structured training is all about repetition and specificity. In executing a training plan, we're throwing specific and repetitive workload at the body in order to convince it to make physiological adaptations. In basic terms, the desired adaptations are increasing the body's ability to do work for longer and at higher intensity for reduced physiological cost
Tapering
I have noticed over years of coaching both road and trail running athletes, one of the biggest differences when they start is their general idea of structured training. I don’t have scientific data backing for this observation, but it seems for the most part that road runners have an easier time sticking to a plan then trail runners do.