I'm amazed that people still practice this kind of destruction. Educated professionals recognize that topping is bad for a tree's health. Topping hinders a tree's ability to produce food through photosynthesis. Trees suddenly exposed to strong sun may experience scalding of bark, which creates entries for destructive pests. Changes in sunlight exposure may also affect neighboring trees and shrubs.
Large stubs have difficulty healing and are vulnerable to insects and diseases.
New limbs are more weakly attached and subject to breakage. Topping has an opposite effect on the goal of reducing height. The water sprouts that result grow rapidly, so the tree quickly returns to its original height and has a weaker but denser crown. A topped tree never regains the original grace and character of its species. We are all robbed of a beautiful asset when a tree is topped.