All too often, landscapers and homeowners rely on hedge trimmers to maintain plant size and height. The problem with this approach is a very dense, unnatural looking shrub where all the foliage is only at the outer most edges of the plant. A plant that is so dense is a perfect environment for diseases and insects to set up camp. Also, trimming a plant with hedge trimmers makes controlling height even more difficult because all those new little branches love to push a lot of growth.
Source: Designing Eden