The amount of time that a landscape looks pristine greatly varies. Each situation needs to be evaluated on a case-by-case basis. As a general rule, after about 20 years, many shrubs can be overgrown, or may be dying from disease. At this point, it makes sense to have the shrubs and other plants removed and start over with a new landscape.
Overgrown shrubs and ornamental trees can block the view of the house from the street, and can prevent people from seeing outside the windows. Additionally, overgrown shrubs can present a safety hazard if they block walkways. Sometimes, the shrubs are significantly overgrown to the point that trimming them back to the desired height and width would result in bare branches that would not produce new growth. At this point, shrub removal makes sense.
A whole new landscape can be created. Quite often, a landscape design is needed so that the new landscape can be properly planned. One thing that experienced landscape designers know is to make sure to select suitable plant material for the location. This way, the plantings will last longer, and require less maintenance.