To race fast an athlete must train fast. To train fast an athlete has to be rested. Recovery days are crucial. Feed off of other people. Don't race them, just run with them.
Recovery days are great for building team spirit.
During group runs you can use the energy of the group to carry you along, saving your energy for when its really needed. Trails are much more forgiving on your legs. Single track trails often force a runner to develop the stabilizing muscles that help with balance and agility. Trail running is to road running what using free weights is to using machines. You get a better total muscle workout without the pounding.