Pruning should be performed after seasonal growth is complete.  You’ll know when seasonal growth is complete when your trees are full of leaves. In slowing growth by trimming, you reduce the total leaf surface, thereby reducing the amount of food manufactured and sent to the roots. Limbs that hang down too far under the weight of the leaves will be noticable in the Summer months.  Rain and wind will affect heavy branches and leaves and could lead to broken branches, exposing your tree to diseases.  Trimming branches that are above your roof line may prevent expensive repairs.