Fear is often used to sell topping. It seems easy to convince someone that a large tree is apt to fall on their house and kill someone. Many other questionable reasons are also given for such radical butchery. Unfortunately, almost anyone can top trees. It takes no special training to use a chain saw to remove all the limbs from a tree but most people don't realize the harm this causes.
Trees store food in twigs and limbs.
Removing them depletes a tree's food reserves. This weakens and stresses the tree. As a result, topped trees are more susceptible to disease and insect attack, and sunscald of the bark. New shoots produced at the large stub cuts, use sparse food reserves to grow back. These long, straight shoots are weakly attached and break off easily.