Why cage? Well, the cage helps keep the plant and tomatoes off the ground. Having the leaves and tomatoes just lay on the dirt puts your tomatoes at risk of disease.
Not all tomatoes need to be caged though. If your plant is a deterrent type of tomato. These plants tend to be smaller and one can get away with just using a stake to support the plant. Your taller plants should definitely have a cage to support it besides the staking. The cages come in so many different styles and colors now.
We have square cages in our Community Garden
We use the round cages in our Back Yard Garden