Leaf pruning is primarily applied to deciduous trees that have beautiful
branches and leaves, for example Acer (Maple), Zelkova, Beech, and
Hornbeam. Leaf pruning achieves the same effect as pruning the other parts
of the tree in increasing the number of small branches and leaves. In
addition, it  improves the sunshine and ventilation for young buds and small
branches between the leaves to promote their growth. This also helps to
bring out clearer view of the tree's shape and the inside of the tree, and it
makes branch pruning and bud pruning smoother to carry out.
Leaf pruning allows the lateral buds to stretch and grow and thereby
promotes the growth of new branches and leaves. In this way, it takes only
one year for the tree to develop the branches and leafage that would
otherwise require two years. Moreover, the new branches and leaves are
small for they have only been growing for a short period. Even if the leaves
suffered from pests, you can grow new leaves by leaf pruning.               
How to carry out leaf pruningdepends on the purpose, the
condition of the tree, and the
species of the tree. For
example, for young trees and
those still under bonsai making,
you can prune all the leaves to
increase the number of small
branches and leaves.