Pruning of Granny Smith Apple tree
Pruning is important for the first 3 to 4 years is necessary to establish the basic tree structure.
I suggest you also reduce the number of limbs in the interior of the tree. The rule of thumb is that you should be able to throw a football through the tree after it is pruned.
I suggest that the ends of the major limbs be cut to a strong side limb that is upright, otherwise the tree will grow 2 or three limbs adjacent to the cut spot, resulting in vigorous growth and shading. See attached file.