Hi Travis,
Trainings in zone 1 and zone 2 improve your aerobic capacity. In The beginning , the tendency is to do more trainings in zone 1 to recover and zone 2 to improve aerobic capacity.
With training and the consequent improvement , your aerobic threshold heart rate value will go up, you will need to balance training with more trainings in zone 1 to avoid overreaching or overtraining .
Cheers
Pedro Carvalho