Decorative containers offer interesting ways to grow a wide variety of plants. In a container you can control the soil, vary the watering regime, adjust the amount of sun or shade, group plants for impact - and ungroup them if the idea doesn't work. With decorative containers you can make a sculptural statement in the garden. With plain containers you can build banks of colour and foliage that hide the outlines of the pots - or any other area you want hidden. Some gardens wouldn't even be possible without containers.
People have the urge to garden no matter how unpromising the site.
I regularly walk past plots of land where there is little soil or space. Put pots along the side of the steps. Use pots brimming with plants to hide the edge. Disguise the walls with pot grown shrubs and climbers. Colourful annuals in pots will make the approach more interesting.