To get a sense of the competing nature of these goals, suppose we had N cells, and wanted to arrange them into a piping system.

If we wanted to bring turning costs to zero, we would put the cells in a linear chain from the root.

But the trouble with a linear chain is that the nodes near the tip are far from the root, so there is a significant cost of transporting their needed fluid all the way from the root.

To reduce these transportation costs, we aim to get the cells closer to the root. For example, we could have a main vein, with lots of little branches.

But the branching introduces turning costs.

If we wanted to bring turning costs to zero, we would put the cells in a linear chain from the root.

But the trouble with a linear chain is that the nodes near the tip are far from the root, so there is a significant cost of transporting their needed fluid all the way from the root.

To reduce these transportation costs, we aim to get the cells closer to the root. For example, we could have a main vein, with lots of little branches.

But the branching introduces turning costs.