Some of the knowledge we lose living in urban and suburban areas is how plants naturally grow. As in, how BIG. As a result, we put big shrubs in the garden where little shrubs should go (I tend to make this mistake with Viburnum); and place trees too close to structures or crowd them together.
In this example at a Peninsula elementary school, two redwoods and one Atlas cedar have been triangulated about 8 - 12 feet on center. Now, this would make a nice grove of small ornamental trees such as cherry or crabapple. Or a compact windbreak of columnar specimens such as cottonwood or 'Fastigiata' hornbeam. But come on! These are long-lived forest giants, wanting to spread 50 feet or more. Even if they were to grow this close together in nature, they would probably be successive generations, never really competing with each other for light, water, nutrients and space.
As this trio matures, they will create a maintenance headache for the Arborist who has to keep their limbs pruned clear of each other (with probably unattractive results). Even so, they probably will struggle along together, limp into midlife, and never achieve the cool grove I bet their planters intended.
The lesson here: work with, not against, Mother Nature. She always wins.