A formal vegetable garden might be a consideration for saving space while accomplishing two different purposes. A combined vegetable garden and a designed landscape. However, in this case, it doesn't appear that saving space has anything to do with this garden design. And for that matter, the vegetables here may may as well be a design choice without any intent for consumption.
In a lot of commercial landscapes applications like center street medians, certain vegetables such as flowering Kale are quite commonly used because of their winter interest added to the landscape. With these certain vegetable as a choice for plants, different planting schemes can be rotated in this formal garden idea throughout all four seasons creating a beautiful landscape all year long.