Shrubs are routinely pruned to maintain size, remove old branches and stems that do not flower well and to eliminate dead and dying branches. But don't confuse shearing with pruning. These are very different methods that are used to maintain shrubs.
Shearing is usually done with manual or powered hedge shears and removes a portion of only the new growth each year. Shearing usually alters the natural form of the plant resulting in a dense outer crown and a “rigid” formal appearance. Because only a portion of the new growth is removed, sheared plants become larger each year. It is difficult to maintain the size, health and appearance through frequent shearing. Shearing is usually desirable only on hedges and formal shrub gardens. Late summer or fall shearing may result in winter injury.
Pruning removes current and previous season’s growth using hand pruners. Pruning is the desired method of maintaining the size, shape and health of shrubs. By selective thinning, light and air can penetrate the interior crown, which promotes growth inside the plant. This provides a healthier plant with an informal, natural appearance. By pruning new and old growth, the plant can be maintained at a desired size.