Apple trees should be pruned every year, not only to keep their shape but also to achieve a high yield. Unproductive and unhealthy branches just use up the energy that could go into fruit production.
Dormant pruning is done during the winter, as late as possible, to avoid damage that harsh conditions could cause. In the spring, the apple tree will use a lot of its energy by regenerating new growth. This reduces the energy that would otherwise go into producing fruit.
Summer pruning should be done after budding, but before the end of July, so that healing can take place before the harshest periods of winter. Summer pruning should be used only for thinning, as the removal of branches also removes the tree's ability to produce food.
Tree training incorporates summer and dormant pruning along with training the growth of the young tree so that it needs less pruning as it matures and can be more productive.