Topping trees is an outdated practice that is extremly detrimental to a tree's health. It sends the tree into a shocked state that draws resources in an unnatural way. Often times ppl are trying to control or manage a tree's height or size. When trees are topped they may look managable but they look terrible. Then within the next few years multiple unnatural limbs grow back in place of what was taken off. The tree is now, not only the same height, but also multiple times more clustered. These branches are also weaker and more apt to have problems down the road. If you don't belive me just google tree topping. Don't type in good or bad and see the results for yourself. Also i'd be weary of the tree care professional that reccomends this practice.