Pruning young trees for proper structure will save you big in the long run. Not only can it considerably increase the life of your tree but it will prevent major structural defects that cause failure. Failure that could have very costly and sometime fatal consequences. Young trees seal their wounds much faster than mature trees, decreasing healing which allows for more growth, and closing wounds through which harmful insects & decay causing organisms could be introduced. It is best to do this kind of pruning mid winter when the tree is dormant. Pruning in winter reduces stress on the tree and risk of disease.
Jennifer Hughes, Certified Arborist