I just returned from a very good two-hour program about pruning fruit trees. First we learned about two kinds of pruners.
There are lots of reasons to prune a fruit tree. Height and shape, light in the center of the tree for more fruit, but my favorite reason is for the espalier shape
This traditional European art of pruning is becoming more popular in the USA.
I am working on two, one year old apple trees to get the espalier shapes. They were grafted last spring. Both are in pots and need to get into larger pots with support this spring. Eventually this tree will get planted in the ground with a permanent horizontal support.