I'm on team ground because I have plenty of space to fill; however, I really enjoy choosing plants for, and putting together container groupings as well, many of which I'll eventually use to fill bare spots in the garden beds.
Cannas, tuberous begonias, caladiums, lisianthus, and pansies all perform much better for me if they're in containers. Others that I like in containers are low growing and tiny flowered trailing plants that might be overlooked if they were planted at ground level. Our clay soil is slow-draining, so additionally, just about anything that I grow here that requires perfect drainage must be in a container.
Two thirds of the plants in this photo are in containers which have then been planted into the bed. It's easier to just go ahead and start the cannas indoors in the pots they'll bloom in and then set them in place once it's warm enough outside.
I use a lot of compost in my containers. It really seems to help to reduce the need for frequent watering. A gravel or chicken grit covering between the plants in a container grouping seems to help with maintaining fairly consistent moisture levels and porosity of the surface soil, especially for containers in sunny spots.
Tuberous begonias won't do anything for me at all unless they're pampered with a covered spot on my deck.
Once the summertime perennials are finished blooming potted mums set on stepping stones are great for adding color to the fall border.
Here I am, on team ground, extolling the virtues of container plants!
Perhaps I should go back to sitting on the fence.