While an individual well planted container can be quite impressive, think what might happen if you put several containers together in a group.
Putting containers together that have different heights, textures and styles can have great impact. A group of containers also offers you great flexibility to move them around and rearrange them for different looks. It also offers the chance to take a container "out of service" if it starts to look bad. Generally, this does not affect the overall display.
Putting containers together as a grouping can also have its advantages especially when they are first planted. Newly planted containers often don't have that "full" look right away. By grouping containers closer together, you can give the illusion of fullness. As the containers fill out, they can be spread further apart to present a totally different look. The same number of containers now takes up more square feet and looks like you actually added containers to the display.
Container height can also be varied simply by sitting some containers on overturned pots, bricks or other things to give some elevation.
Placing container groups by the entrance to the home helps to draw attention to the door and act as a sign of welcome. Grouping containers on a porch, balcony or patio has the affect of softening what might be a very stark, open space. It can make the place a refuge from all else that is happening in the world.
While most containers are found as a stand alone element, think about incorporating them into the garden itself. Large, bold containers worked into a flower or shrub border now becomes part of the planting bed. They are looked at as specimen or sculptural accents. The base of the pot is surrounded by annuals or perennials, the container is a piece of art, and it is topped off with a floral display.
Landscaping with containers can be as simple as one well-chosen and planted pot to a group of several pots making a statement and colorizing an otherwise unplantable area.